Publications de l'équipe Instabilités, Turbulence & Contrôle
2017
Philippe Meliga. Harmonics generation and the mechanics of saturation in flow over an open cavity: a second-order self-consistent description. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 826, pp.503 - 521. Plus de détails...
The flow over an open cavity is an example of supercritical Hopf bifurcation leading to periodic limit-cycle oscillations. One of its distinctive features is the existence of strong higher harmonics, which results in the time-averaged mean flow being strongly linearly unstable. For this class of flows, a simplified formalism capable of unravelling how exactly the instability grows and saturates is lacking. This study builds on previous work by Mantic-Lugo et al. (Phys. Rev. Lett., vol. 113, 2014, 084501) to fill in the gap using a parametrized approximation of an instantaneous, phase-averaged mean flow, coupled in a quasi-static manner to multiple linear harmonic disturbances interacting nonlinearly with one another and feeding back on the mean flow via their Reynolds stresses. This provides a self-consistent modelling of the mean flow-fluctuation interaction, in the sense that all perturbation structures are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations. The first harmonic is sought as the superposition of two components, a linear component generated by the instability and aligned along the leading eigenmode of the mean flow, and a nonlinear orthogonal component generated by the higher harmonics, which progressively distorts the linear growth rate and eigenfrequency of the eigenmode. Saturation occurs when the growth rate of the first harmonic is zero, at which point the stabilizing effect of the second harmonic balances exactly the linear instability of the eigenmode. The model does not require any input from numerical or experimental data, and accurately predicts the transient development and the saturation of the instability, as established from comparison to time and phase averages of direct numerical simulation data.
Philippe Meliga. Harmonics generation and the mechanics of saturation in flow over an open cavity: a second-order self-consistent description. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 826, pp.503 - 521. <10.1017/jfm.2017.439>. <hal-01585331>
E. Constant, J. Favier, M. Meldi, P. Meliga, E. Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers & Fluids, 2017, 157, pp.55 - 72. Plus de détails...
The present work proposes a modified Pressure-Implicit Split-Operator (PISO) solver integrating the recent Immersed Boundary Method (IBM) proposed by Pinelli et al. [1] in order to perform reliable simulations of incompressible flows around bluff bodies using the open source toolbox OpenFOAM version 2.2 (ESI-OpenCFD [2]). The (IBM) allows for a precise representation of fixed and moving solid obstacles embedded in the physical domain, using uniform or stretched Cartesian meshes. Owing to this feature, the maximum level of accuracy and scalability of the numerical solvers can be systematically achieved. An iterative scheme based on sub-iterations between (IBM) and pressure correction has been implemented in the native (PISO) solver of OpenFOAM. This allows one to use fast optimized Poisson solvers while satisfying simultaneously the divergence-free flow state and the no-slip condition at the body surface. To compute the divergence of the momentum equation (in the PISO loop) and the interpolation of the fluxes, we propose an hybrid calculation with an analytical resolution (using the kernel function equation) of the quantities involving the force term (singular quantities). A careful and original verification study has been carried out which allows to estimate three different errors related to the discretization and to the (IBM). Various 2D and 3D well-documented test cases of academic flows around fixed or moving cylinders have been simulated and carefully validated against existing data from the literature in a large range of Reynolds numbers, Re = 30 − 3900 and in the frame of DNS and DDES OpenFOAM native models.
E. Constant, J. Favier, M. Meldi, P. Meliga, E. Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers & Fluids, 2017, 157, pp.55 - 72. <10.1016/j.compfluid.2017.08.001>. <hal-01591562>
Vincent Mons, Jean-Camille Chassaing, Pierre Sagaut. Optimal sensor placement for variational data assimilation of unsteady flows past a rotationally oscillating cylinder. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 823, pp.230 - 277. Plus de détails...
Vincent Mons, Jean-Camille Chassaing, Pierre Sagaut. Optimal sensor placement for variational data assimilation of unsteady flows past a rotationally oscillating cylinder. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 823, pp.230 - 277. <10.1017/jfm.2017.313>. <hal-01548417>
Congshan Zhuo, Pierre Sagaut. Acoustic multipole sources for the regularized lattice Boltzmann method: Comparison with multiple-relaxation-time models in the inviscid limit. Physical Review E , American Physical Society (APS), 2017, 95 (6), pp.063301. Plus de détails...
Congshan Zhuo, Pierre Sagaut. Acoustic multipole sources for the regularized lattice Boltzmann method: Comparison with multiple-relaxation-time models in the inviscid limit. Physical Review E , American Physical Society (APS), 2017, 95 (6), pp.063301. <10.1103/PhysRevE.95.063301>. <hal-01548424>
M. Meldi, Pierre Sagaut. Turbulence in a box: quantification of large-scale resolution effects in isotropic turbulence free decay. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 818, pp.697 - 715. Plus de détails...
The effects of the finiteness of the physical domain over the free decay of homogeneous isotropic turbulence are explored in the present article. Saturation at the large scales is investigated by the use of theoretical analysis and eddy-damped quasi-normal Markovian calculations. Both analyses indicate a strong sensitivity of the large-scale features of the flow to saturation and finite Reynolds number effects. This aspect plays an important role in the general lack of agreement between grid turbulence experiments and numerical simulations. On the other hand, the statistical quantities associated with the behaviour of the spectrum in the inertial region are only marginally affected by saturation. These results suggest new guidelines for the interpretation of experimental and direct numerical simulation studies.
M. Meldi, Pierre Sagaut. Turbulence in a box: quantification of large-scale resolution effects in isotropic turbulence free decay. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 818, pp.697 - 715. <10.1017/jfm.2017.158>. <hal-01527613>
Xun Wang, Shahram Khazaie, Luca Margheri, Pierre Sagaut. Shallow water sound source localization using the iterative beamforming method in an image framework. Journal of Sound and Vibration, Elsevier, 2017, 395, pp.354 - 370. Plus de détails...
Shallow water is a complicated sound propagation medium due to multiple reflections by water surface and bottom, imprecisely measured sound speed, noisy environment, etc. Therefore, in order to localize a shallow water sound source, classical signal processing techniques must be improved by taking these complexities into account. In this work, the multiple reflections and uncertain reflectivity of water bottom are explicitly modeled. In the proposed model, a measured signal is a mixture of the direct propagation from the source and the multiple reflections. Instead of solving the Helmholtz equation with boundary conditions of reflections, each signal is interpreted as a superposition of signals emitting from the physical source and its image sources in a free space, which results in a fast computation of sound propagation. Then, the source location, along with its amplitude, reflection paths and power loss of bottom reflection, is estimated via the iterative beamforming (IB) method, which alternatively estimates the source contributions and performs beamforming on these estimates until convergence. This approach does not need to compute the sound propagation for all the possible source locations in a large space, which thus leads to a low computational cost. Finally, numerical simulations are introduced to illustrate the advantage of the proposed model and the source estimation method. The sensitivity of the proposed method with respect to model parameter uncertainties is also investigated via a full uncertainty quantification analysis. The localization error of IB is proved to be acceptable in the given error range of sound speed and water depth. Besides, the IB source estimate is more sensitive to the sound speed while the matched-field processing methods have a stronger sensitivity to the water depth: this result can guide the choice of source localization method in different cases of model parameter uncertainties.
Xun Wang, Shahram Khazaie, Luca Margheri, Pierre Sagaut. Shallow water sound source localization using the iterative beamforming method in an image framework. Journal of Sound and Vibration, Elsevier, 2017, 395, pp.354 - 370. <10.1016/j.jsv.2017.02.032>. <hal-01527615>
The spectral analysis is a basic tool to characterise the behaviour of any convection scheme. By nature, the solution projected onto the Fourier basis enables to estimate the dissipation and the dispersion associated with the spatial discretisation of the hyperbolic linear problem. In this paper, we wish to revisit such analysis, focusing attention on two key points. The first point concerns the effects of time integration on the spectral analysis. It is shown with standard high-order Finite Difference schemes dedicated to aeroacoustics that the time integration has an effect on the required number of points per wavelength. The situation depends on the choice of the coupled schemes (one for time integration, one for space derivative and one for the filter) and here, the compact scheme with its eighth-order filter seems to have a better spectral accuracy than the considered dispersion relation preserving scheme with its associated filter, especially in terms of dissipation. Secondly, such a coupled space time approach is applied to the new class of high-order spectral discontinuous approaches, focusing especially on the Spectral Difference method. A new way to address the specific spectral behaviour of the scheme is introduced first for wavenumbers in [0,pi], following the Matrix Power method. For wavenumbers above pi, an aliasing phenomenon always occurs but it is possible to understand and to control the aliasing of the signal. It is shown that aliasing depends on the polynomial degree and on the number of time steps. A new way to define dissipation and dispersion is introduced and applied to wavenumbers larger than it. Since the new criteria recover the previous results for wavenumbers below it, the new proposed approach is an extension of all the previous ones dealing with dissipation and dispersion errors. At last, since the standard Finite Difference schemes can serve as reference solution for their capability in aeroacoustics, it is shown that the Spectral Difference method is as accurate as (or even more accurate) than the considered Finite Difference schemes.
Julien Vanharen, Guillaume Puigt, Xavier Vasseur, Jean-François Boussuge, Pierre Sagaut. Revisiting the spectral analysis for high-order spectral discontinuous methods. Journal of Computational Physics, Elsevier, 2017, 337, pp.379 - 402. <10.1016/j.jcp.2017.02.043>. <hal-01527618>
Yosuke Anzai, Koji Fukagata, Philippe Meliga, Edouard Boujo, François Gallaire. Numerical simulation and sensitivity analysis of a low-Reynolds-number flow around a square cylinder controlled using plasma actuators. Physical Review Fluids, American Physical Society, 2017, 2 (4), . Plus de détails...
Flow around a square cylinder controlled using plasma actuators (PAs) is numerically investigated by direct numerical simulation in order to clarify the most effective location of actuator installation and to elucidate the mechanism of control effect. The Reynolds number based on the cylinder diameter and the free-stream velocity is set to be 100 to study the fundamental effect of PAs on two-dimensional vortex shedding, and three different locations of PAs are considered. The mean drag and the root-mean-square of lift fluctuations are found to be reduced by 51% and 99% in the case where two opposing PAs are aligned vertically on the rear surface. In that case, a jet flow similar to a base jet is generated by the collision of the streaming flows induced by the two opposing PAs, and the vortex shedding is completely suppressed. The simulation results are ultimately revisited in the frame of linear sensitivity analysis, whose computational cost is much lower than that of performing the full simulation. A good agreement is reported for low control amplitudes, which allows further discussion of the linear optimal arrangement for any number of PAs.
Yosuke Anzai, Koji Fukagata, Philippe Meliga, Edouard Boujo, François Gallaire. Numerical simulation and sensitivity analysis of a low-Reynolds-number flow around a square cylinder controlled using plasma actuators. Physical Review Fluids, American Physical Society, 2017, 2 (4), <10.1103/PhysRevFluids.2.043901>. <hal-01585359>
Zhe Li, Julien Favier. A non-staggered coupling of finite element and lattice Boltzmann methods via an immersed boundary scheme for fluid-structure interaction. Computers and Fluids, Elsevier, 2017, 143, pp.90 - 102. Plus de détails...
The paper presents a numerical framework for the coupling of finite element and lattice Boltzmann methods for transient problems involving fluid-structure interaction. The solid structure is discretized with the finite element method and integrated in time with the explicit Newmark scheme. The lattice Boltzmann method is used for the simulation of single-component weakly-compressible fluid flows. The two numerical methods are coupled via a direct-forcing immersed boundary method in a non-staggered way. Without subiteration within each time-step, the proposed method can ensure the synchronization of the time integrations, and thus the strong coupling of both subdomains by resolving a linear system of coupling equations at each time-step. Hence the energy transfer at the fluid-solid interface is correct, i.e. neither energy dissipation nor energy injection will occur at the interface, which can retain the numerical stability. A well-known fluid-structure interaction test case is adopted to validate the proposed coupling method. It is shown that the stability of the used numerical schemes can be preserved and a good agreement is found with the reference results.
Zhe Li, Julien Favier. A non-staggered coupling of finite element and lattice Boltzmann methods via an immersed boundary scheme for fluid-structure interaction. Computers and Fluids, Elsevier, 2017, 143, pp.90 - 102. <10.1016/j.compfluid.2016.11.008>. <hal-01403915>
Shahram Khazaie, Régis Cottereau, Didier Clouteau. Numerical observation of the equipartition regime in a 3D random elastic medium, and discussion of the limiting parameters. Computers and Geosciences, Elsevier, 2017, 102, pp.56-67. Plus de détails...
At long lapse times in the weakly scattering regime, the energy of the coda in a randomly fluctuating isotropic medium is equipartitioned between P and S modes. This behavior is well understood mathematically and physically for full spaces. For realistic domains, analytical results are more scarce and numerical simulations become a valuable tool. This paper discusses, based on numerical simulations of wave propagation in a 3D randomly heterogeneous elastic medium, the transition to an equipartitioned regime of the wave field. Both the time to transition and the value of the ratio of energies after transition are evaluated. Several influencing parameters are discussed, either physical (ratio of background P-and S-velocities, propagation length, variance of the heterogeneities) or numerical (influence of Perfectly Matched Layers). Setting up of a localization regime, inefficient mixture of body waves and small propagation length compared to the transport mean free paths are identified as constraining for the transition toward an equipartition regime.
Shahram Khazaie, Régis Cottereau, Didier Clouteau. Numerical observation of the equipartition regime in a 3D random elastic medium, and discussion of the limiting parameters. Computers and Geosciences, Elsevier, 2017, 102, pp.56-67. <10.1016/j.cageo.2017.02.007>. <hal-01473195>
Philippe Meliga, Olivier Cadot, Eric Serre. Experimental and Theoretical Sensitivity Analysis of Turbulent Flow Past a Square Cylinder. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2016, 97 (4, SI), pp.987-1015. Plus de détails...
We assess experimentally and theoretically the ability of a small control cylinder to alter vortex shedding in turbulent flow past a square cylinder at R e = 22,000. Results are presented in terms of sensitivity maps showing the flow regions where the shedding frequency and amplitude are most affected by the control cylinder. Experimental results are obtained for a ratio 0.02 of the cylinder diameters, over an extended domain covering the wake, the shear layers and the free stream. The shedding frequency can be either decreased or increased, the largest effects being obtained placing the control cylinder at the outer edge of the detached shear layers (associated with frequency decrease) or upstream of the square cylinder (associated with frequency increase, in contrast with previous results obtained for a D-shaped geometry of the main cylinder). In contrast, the oscillation amplitude is rarely decreased, meaning that any variation of the shedding frequency comes at the expense of more intense vortex shedding. These findings are revisited in the frame of a theoretical, linear sensitivity analysis of the time-averaged mean flow, performed using adjoint methods in the frame of Reynolds-averaged Navier-Stokes modeling. We show that the retained approach carries valuable information in view of guiding efficient control strategy, as it allows identifying the main regions yielding either a decrease or an increase of the shedding frequency in striking agreement with the experiments. This is a tremendous timesaving in so far as the controlled states need not be computed, the overall computational cost being roughly that of computing the mean flow. In contrast, performing the sensitivity analysis on the underlying unstable steady state yields flawed predictions, hence stressing the need to encompass some level of mean coherent-coherent perturbations interaction in the linear model.
Philippe Meliga, Olivier Cadot, Eric Serre. Experimental and Theoretical Sensitivity Analysis of Turbulent Flow Past a Square Cylinder. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2016, 97 (4, SI), pp.987-1015. <10.1007/s10494-016-9755-0>. <hal-01461791>
François Gallaire, Edouard Boujo, Vladislav Mantic-Lugo, Cristobal Arratia, Benjamin Thiria, et al.. Pushing amplitude equations far from threshold: application to the supercritical Hopf bifurcation in the cylinder wake. Fluid Dynamics Research, IOP Publishing, 2016, 48 (6), . Plus de détails...
The purpose of this review article is to push amplitude equations as far as possible from threshold. We focus on the Stuart-Landau amplitude equation describing the supercritical Hopf bifurcation of the flow in the wake of a cylinder for critical Reynolds number Re-c approximate to 46. After having reviewed Stuart's weakly nonlinear multiple-scale expansion method, we first demonstrate the crucial importance of the choice of the critical parameter. For the wake behind a cylinder considered in this paper, choosing. is an element of(2) = Re-c(1)-Re-c(-1) instead of is an element of'(2) = Re-Re-c/Re-c(2) considerably improves the prediction of the Landau equation. Although Sipp and Lebedev (2007 J. Fluid Mech 593 333-58) correctly identified the adequate bifurcation parameter is an element of, they have plotted their results adding an additional linearization, which amounts to using. is an element of' as approximation to is an element of'. We then illustrate the risks of calculating `running' Landau constants by projection formulas at arbitrary values of the control parameter. For the cylinder wake case, this scheme breaks down and diverges close to Re approximate to 100. We propose an interpretation based on the progressive loss of the non-resonant compatibility condition, which is the cornerstone of Stuart's multiple-scale expansion method. We then briefly review a self-consistent model recently introduced in the literature and demonstrate a link between its properties and the above-mentioned failure.
François Gallaire, Edouard Boujo, Vladislav Mantic-Lugo, Cristobal Arratia, Benjamin Thiria, et al.. Pushing amplitude equations far from threshold: application to the supercritical Hopf bifurcation in the cylinder wake. Fluid Dynamics Research, IOP Publishing, 2016, 48 (6), <10.1088/0169-5983/48/6/061401>. <hal-01461792>
Luca Margheri, Pierre Sagaut. A hybrid anchored-ANOVA - POD/Kriging method for uncertainty quantification in unsteady high-fidelity CFD simulations. Journal of Computational Physics, Elsevier, 2016, 324, pp.137-173. Plus de détails...
To significantly increase the contribution of numerical computational fluid dynamics (CFD) simulation for risk assessment and decision making, it is important to quantitatively measure the impact of uncertainties to assess the reliability and robustness of the results. As unsteady high-fidelity CFD simulations are becoming the standard for industrial applications, reducing the number of required samples to perform sensitivity (SA) and uncertainty quantification (UQ) analysis is an actual engineering challenge. The novel approach presented in this paper is based on an efficient hybridization between the anchored-ANOVA and the POD/Kriging methods, which have already been used in CFD-UQ realistic applications, and the definition of best practices to achieve global accuracy. The anchored-ANOVA method is used to efficiently reduce the UQ dimension space, while the POD/Kriging is used to smooth and interpolate each anchored-ANOVA term. The main advantages of the proposed method are illustrated through four applications with increasing complexity, most of them based on Large-Eddy Simulation as a high-fidelity CFD tool: the turbulent channel flow, the flow around an isolated bluff-body, a pedestrian wind comfort study in a full scale urban area and an application to toxic gas dispersion in a full scale city area. The proposed c-APK method (anchored-ANOVA-POD/Kriging) inherits the advantages of each key element: interpolation through POD/Kriging precludes the use of quadrature schemes therefore allowing for a more flexible sampling strategy while the ANOVA decomposition allows for a better domain exploration. A comparison of the three methods is given for each application. In addition, the importance of adding flexibility to the control parameters and the choice of the quantity of interest (QoI) are discussed. As a result, global accuracy can be achieved with a reasonable number of samples allowing computationally expensive CFD-UQ analysis. (C) 2016 Elsevier Inc. All rights reserved.
Luca Margheri, Pierre Sagaut. A hybrid anchored-ANOVA - POD/Kriging method for uncertainty quantification in unsteady high-fidelity CFD simulations. Journal of Computational Physics, Elsevier, 2016, 324, pp.137-173. <10.1016/j.jcp.2016.07.036>. <hal-01461789>
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, Elsevier, 2016, 321, pp.606-623. Plus de détails...
The new code TOKAM3X simulates plasma turbulence in full torus geometry including the open field lines of the Scrape-off Layer (SOL) and the edge closed field lines region in the vicinity of the separatrix. Based on drift-reduced Braginskii equations, TOKAM3X is able to simulate both limited and diverted plasmas. Turbulence is flux driven by incoming particles from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed so that interactions between large scale flows and turbulence are consistently treated. Based on a domain decomposition, specific numerical schemes are proposed using conservative finite-differences associated to a semi-implicit time advancement. The process computation is multi-threaded and based on MPI and OpenMP libraries. In this paper, fluid model equations are presented together with the proposed numerical methods. The code is verified using the manufactured solution technique and validated through documented simple experiments. Finally, first simulations of edge plasma turbulence in X-point geometry are also introduced in a JET geometry. (C) 2016 Elsevier Inc. All rights reserved.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, Elsevier, 2016, 321, pp.606-623. <10.1016/j.jcp.2016.05.038>. <hal-01461797>
Philippe Meliga, Edouard Boujo, François Gallaire. A self-consistent formulation for the sensitivity analysis of finite-amplitude vortex shedding in the cylinder wake. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2016, 800, pp.327-357. Plus de détails...
We use the adjoint method to compute sensitivity maps for the limit-cycle frequency and amplitude of the Benard von Karmzin vortex street in the wake of a circular cylinder. rfhe sensitivity, analysis is performed in the frame of the semi-linear self consistent model recently introduced by Mamie et al. (Phys. Rev. Lett., vol. 113, 2014, 084501), which allows us to describe accurately the effect of the control on the mean flow-, but also on the finite-amplitude fluctuation that couples back nonlinearly onto the mean flow via the formation of Reynolds stress. The sensitivity is computed with respect to arbitrary steady and synchronous time-harmonic body forces. For a small amplitude of the control, the theoretical variations of the limit-cycle frequency predict well those of the controlled flow, as obtained from either self-consistent modelling or direct numerical simulation of the Navier Stokes equations. This is not the case if the variations are computed in the simpler mean flow approach overlooking the coupling between the mean and fluctuating components of the flow- perturbation induced by the control. The variations of the limit-cycle amplitude (that falls out the scope of the mean flow approach) are also correctly predicted, meaning that the approach can serve as a relevant and systematic guideline to control strongly unstable flows exhibiting non-small, finite amplitudes of oscillation. As an illustration, we apply the method to control by means of a small secondary control cylinder and discuss the obtained results in the light of the seminal experiments of Strykowski & Sreenivasan
Philippe Meliga, Edouard Boujo, François Gallaire. A self-consistent formulation for the sensitivity analysis of finite-amplitude vortex shedding in the cylinder wake. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2016, 800, pp.327-357. <10.1017/jfm.2016.390>. <hal-01461794>
Vincent Mons, Jean-Camille Chassaing, Thomas Gomez, Pierre Sagaut. Reconstruction of unsteady viscous flows using data assimilation schemes. Journal of Computational Physics, Elsevier, 2016, 316, pp.255-280. Plus de détails...
This paper investigates the use of various data assimilation (DA) approaches for the reconstruction of the unsteady flow past a cylinder in the presence of incident coherent gusts. Variational, ensemble Kalman filter-based and ensemble-based variational DA techniques are deployed along with a 2D compressible Navier–Stokes flow solver, which is also used to generate synthetic observations of a reference flow. The performance of these DA schemes is thoroughly analyzed for various types of observations ranging from the global aerodynamic coefficients of the cylinder to the full 2D flow field. Moreover, different reconstruction scenarios are investigated in order to assess the robustness of these methods for large scale DA problems with up to 105 control variables. In particular, we show how an iterative procedure can be used within the framework of ensemble-based methods to deal with both non-uniform unsteady boundary conditions and initial field reconstruction. The different methodologies developed and assessed in this work give a review of what can be done with DA schemes in computational fluid dynamics (CFD) paradigm. In the same time, this work also provides useful information which can also turn out to be rational arguments in the DA scheme choice dedicated to a specific CFD application.
Vincent Mons, Jean-Camille Chassaing, Thomas Gomez, Pierre Sagaut. Reconstruction of unsteady viscous flows using data assimilation schemes. Journal of Computational Physics, Elsevier, 2016, 316, pp.255-280. <10.1016/j.jcp.2016.04.022>. <hal-01333881>
Marianna Pepona, Julien Favier. A coupled Immersed Boundary – Lattice Boltzmann method for incompressible flows through moving porous media A coupled Immersed Boundary -Lattice Boltzmann method for incompressible flows through moving porous media. Journal of Computational Physics, Elsevier, 2016, . Plus de détails...
In this work, we propose a numerical framework to simulate fluid flows in interaction with moving porous media of complex geometry. It is based on the Lattice Boltzmann method including porous effects via a Brinkman-Forchheimer-Darcy force model coupled to the Immersed Boundary method to handle complex ge-ometries and moving structures. The coupling algorithm is described in detail and it is validated on well-established literature test cases for both stationary and moving porous configurations. The proposed method is easy to implement and efficient in terms of CPU cost and memory management compared to alternative methods which can be used to deal with moving immersed porous media, e.g. re-meshing at each time step or use of a moving/chimera mesh. An overall good agreement was obtained with reference results, opening the way to the numerical simulation of moving porous media for flow control applications.
Marianna Pepona, Julien Favier. A coupled Immersed Boundary – Lattice Boltzmann method for incompressible flows through moving porous media A coupled Immersed Boundary -Lattice Boltzmann method for incompressible flows through moving porous media. Journal of Computational Physics, Elsevier, 2016, <10.1016/j.jcp.2016.06.026>. <hal-01336315>
Antoine Briard, Thomas Gomez, Vincent Mons, Pierre Sagaut. Decay and growth laws in homogeneous shear turbulence. Journal of Turbulence, Taylor & Francis, 2016, 17 (7), pp.699 - 726. Plus de détails...
Homogeneous anisotropic turbulence has been widely studied in the past decades, both numerically and experimentally. Shear flows have received a particular attention because of the numerous physical phenomena they exhibit. In the present paper, both the decay and growth of anisotropy in homogeneous shear flows at high Reynolds numbers are revisited thanks to a recent eddy-damped quasi-normal Markovian (EDQNM) closure adapted to homogeneous anisotropic turbulence. The emphasis is put on several aspects: an asymptotic model for the slow-part of the pressure-strain tensor is derived for the return to isotropy process when mean-velocity gradients are released. Then, a general decay law for purely anisotropic quantities in Batchelor turbulence is proposed. At last, a discussion is proposed to explain the scattering of global quantities obtained in DNS and experiments in sustained shear flows: the emphasis is put on the exponential growth rate of the kinetic energy and on the shear parameter.
Antoine Briard, Thomas Gomez, Vincent Mons, Pierre Sagaut. Decay and growth laws in homogeneous shear turbulence. Journal of Turbulence, Taylor & Francis, 2016, 17 (7), pp.699 - 726. <10.1080/14685248.2016.1191641>. <hal-01429646>
Yongliang Feng, Pierre Sagaut, Wen-Quan Tao. A compressible lattice Boltzmann finite volume model for high subsonic and transonic flows on regular lattices. Computers and Fluids, Elsevier, 2016, 131, pp.45-55. Plus de détails...
A multi-dimensional double distribution function thermal lattice Boltzmann model has been developed to simulate fully compressible flows at moderate Mach number. The lattice Boltzmann equation is temporally and spatially discretizated by an asymptotic preserving finite volume scheme. The micro-velocities discretization is adopted on regular low-symmetry lattices (D1Q3, D2Q9, D3Q15, D3Q19, D3Q27). The third-order Hermite polynomial density distribution function on low-symmetry lattices is used to solve the flow field, while a second-order energy distribution is employed to compute the temperature field. The fully compressible Navier-Stokes equations are recovered by standard order Gauss-Hermite polynomial expansions of Maxwell distribution with cubic correction terms, which are added by an external force expressed in orthogonal polynomials form. The proposed model is validated considering several benchmark cases, namely the Sod shock tube, thermal Couette flow and two-dimensional Riemann problem. The numerical results are in very good agreement with both analytical solution and reference results. (C) 2016 Elsevier Ltd. All rights reserved.
Yongliang Feng, Pierre Sagaut, Wen-Quan Tao. A compressible lattice Boltzmann finite volume model for high subsonic and transonic flows on regular lattices. Computers and Fluids, Elsevier, 2016, 131, pp.45-55. <10.1016/j.compfluid.2016.03.009>. <hal-01461781>
Fabio Riva, Clothilde Colin, Julien Denis, Luke Easy, Ivo Furno, et al.. Blob dynamics in the TORPEX experiment: a multi-code validation. Plasma Physics and Controlled Fusion, IOP Publishing, 2016, 58 (4), . Plus de détails...
Three-dimensional and two-dimensional seeded blob simulations are performed with five different fluid models, all based on the drift-reduced Braginskii equations, and the numerical results are compared among themselves and validated against experimental measurements provided by the TORPEX device ( Fasoli et al 2006 Phys. Plasmas 13 055902). The five models are implemented in four simulation codes, typically used to simulate the plasma dynamics in the tokamak scrape-off layer, namely BOUT++ (Dudson et al 2009 Comput. Phys. Commun. 180 1467), GBS (Ricci et al 2012 Plasma Phys. Control. Fusion 54 124047), HESEL (Nielsen et al 2015 Phys. Lett. A 379 3097), and TOKAM3X (Tamain et al 2014 Contrib. Plasma Phys. 54 555). Three blobs with different velocities and different stability properties are simulated. The differences observed among the simulation results and the different levels of agreement with experimental measurements are investigated, increasing our confidence in our simulation tools and shedding light on the blob dynamics. The comparisons demonstrate that the radial blob dynamics observed in the three-dimensional simulations is in good agreement with experimental measurements and that, in the present experimental scenario, the two-dimensional model derived under the assumption of k(vertical bar vertical bar) = 0 is able to recover the blob dynamics observed in the three-dimensional simulations. Moreover, it is found that an accurate measurement of the blob temperature is important to perform reliable seeded blob simulations.
Fabio Riva, Clothilde Colin, Julien Denis, Luke Easy, Ivo Furno, et al.. Blob dynamics in the TORPEX experiment: a multi-code validation. Plasma Physics and Controlled Fusion, IOP Publishing, 2016, 58 (4), <10.1088/0741-3335/58/4/044005>. <hal-01461784>
Seung-Bu Park, Pierre Gentine, Kai Schneider, Marie Farge. Coherent Structures in the Boundary and Cloud Layers: Role of Updrafts, Subsiding Shells, and Environmental Subsidence. Journal of the Atmospheric Sciences, American Meteorological Society, 2016, 73 (4), pp.1789-1814. Plus de détails...
Coherent structures, such as updrafts, downdrafts/shells, and environmental subsidence in the boundary and cloud layers of shallow convection, are investigated using a new classification method. Using large-eddy simulation data, the new method first filters out background turbulence and small-scale gravity waves from the coherent part of the flow, composed of turbulent coherent structures and large-scale transporting gravity waves. Then the algorithm divides this coherent flow into ``updrafts,'' ``downdrafts/shells,'' ``subsidence,'' ``ascendance,'' and four other flow structures using an octant analysis. The novel method can systematically track structures from the cloud-free boundary layer to the cloud layer, thus allowing systematic analysis of the fate of updrafts and downdrafts. The frequency and contribution of the coherent structures to the vertical mass flux and transport of heat and moisture can then be investigated for the first time. Updrafts, subsidence, and downdrafts/subsiding shells-to a lesser extent-are shown to be the most frequent and dominant contributors to the vertical transport of heat and moisture in the boundary layer. Contrary to previous perspective, environmental subsidence transport is shown to be weak in the cloud layer. Instead, downdrafts/shells are the main downward transport contributors, especially in the trade inversion layer. The newly developed method in this study can be used to better evaluate the entrainment and detrainment of individual-or an ensemble of-coherent structures from the unsaturated boundary layer to the cloud layer.
Seung-Bu Park, Pierre Gentine, Kai Schneider, Marie Farge. Coherent Structures in the Boundary and Cloud Layers: Role of Updrafts, Subsiding Shells, and Environmental Subsidence. Journal of the Atmospheric Sciences, American Meteorological Society, 2016, 73 (4), pp.1789-1814. <10.1175/JAS-D-15-0240.1>. <hal-01461782>
Amaury Bannier, Eric Garnier, Pierre Sagaut. Friction drag reduction achievable by near-wall turbulence manipulation in spatially developing boundary-layer. Physics of Fluids, American Institute of Physics, 2016, 28 (035108), 16 p. Plus de détails...
Various control strategies, such as active feedback control or riblets, end up restraining near-wall turbulence. An analytical study is conducted to estimate the drag-reduction achievable by such control in zero-pressure-gradient turbulent boundary-layers. Based on an idealized control which damps all fluctuations within a near-wall layer, a composite flow profile is established. It leads to explicit models for both the drag-reduction and the boundary-layer development rate. A skin-friction decomposition is applied and gives physical insights on the underlying phenomena. The control is found to alter the spatial development of the boundary-layer, resulting in detrimental impact on the skin-friction. However, the drag-reducing mechanism, attributed to the turbulence weakening, is found predominant and massive drag reductions remain achievable at high Reynolds number, although a minute part of the boundary-layer is manipulated. The model is finally assessed against Large Eddy Simulations of riblet-controlled flow.
Amaury Bannier, Eric Garnier, Pierre Sagaut. Friction drag reduction achievable by near-wall turbulence manipulation in spatially developing boundary-layer. Physics of Fluids, American Institute of Physics, 2016, 28 (035108), 16 p. <10.1063/1.4943625>. <hal-01428632>
Dmitry Kolomenskiy, Masateru Maeda, Thomas Engels, Hao Liu, Kai Schneider, et al.. Aerodynamic Ground Effect in Fruitfly Sized Insect Takeoff. PLoS ONE, Public Library of Science, 2016, 11 (3), pp.e0152072. Plus de détails...
Aerodynamic ground effect in flapping-wing insect flight is of importance to comparative morphologies and of interest to the micro-air-vehicle (MAV) community. Recent studies, however, show apparently contradictory results of either some significant extra lift or power savings, or zero ground effect. Here we present a numerical study of fruitfly sized insect takeoff with a specific focus on the significance of leg thrust and wing kinematics. Flapping-wing takeoff is studied using numerical modelling and high performance computing. The aerodynamic forces are calculated using a three-dimensional Navier--Stokes solver based on a pseudo-spectral method with volume penalization. It is coupled with a flight dynamics solver that accounts for the body weight, inertia and the leg thrust, while only having two degrees of freedom: the vertical and the longitudinal horizontal displacement. The natural voluntary takeoff of a fruitfly is considered as reference. The parameters of the model are then varied to explore possible effects of interaction between the flapping-wing model and the ground plane. These modified takeoffs include cases with decreased leg thrust parameter, and/or with periodic wing kinematics, constant body pitch angle. The results show that the ground effect during natural voluntary takeoff is negligible. In the modified takeoffs, when the rate of climb is slow, the difference in the aerodynamic forces due to the interaction with the ground is up to 6%. Surprisingly, depending on the kinematics, the difference is either positive or negative, in contrast to the intuition based on the helicopter theory, which suggests positive excess lift. This effect is attributed to unsteady wing-wake interactions. A similar effect is found during hovering.
Dmitry Kolomenskiy, Masateru Maeda, Thomas Engels, Hao Liu, Kai Schneider, et al.. Aerodynamic Ground Effect in Fruitfly Sized Insect Takeoff. PLoS ONE, Public Library of Science, 2016, 11 (3), pp.e0152072. <10.1371/journal.pone.0152072>. <hal-01299261>
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga. A Powell-Sabin finite element scheme for partial differential equations . ESAIM: Proceedings, EDP Sciences, 2016, 53, pp.64-76. Plus de détails...
In this paper are analyzed finite element methods based on Powell-Sabin splines, for the solution of partial differential equations in two dimensions. PS splines are piecewise quadratic polynomials defined on a triangulation of the domain, and exhibit a global C 1 continuity. Critical issues when dealing with PS splines, and described in this work, are the construction of the shape functions and the imposition of the boundary conditions. The PS finite element method is used at first to solve an elliptic problem describing plasma equilibrium in a tokamak. Finally, a transient convective problem is also considered, and a stabilized formulation is presented.
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga. A Powell-Sabin finite element scheme for partial differential equations . ESAIM: Proceedings, EDP Sciences, 2016, 53, pp.64-76. <10.1051/proc/201653005>. <hal-01377903>
Luc Di Gallo, Cédric Reux, Frédéric Imbeaux, Jean-François Artaud, Michal Owsiak, et al.. Coupling between a multi-physics workflow engine and an optimization framework. Computer Physics Communications, Elsevier, 2016, 200, pp.76-86. Plus de détails...
A generic coupling method between a multi-physics workflow engine and an optimization framework is presented in this paper. The coupling architecture has been developed in order to preserve the integrity of the two frameworks. The objective is to provide the possibility to replace a framework, a workflow or an optimizer by another one without changing the whole coupling procedure or modifying the main content in each framework. The coupling is achieved by using a socket-based communication library for exchanging data between the two frameworks. Among a number of algorithms provided by optimization frameworks, Genetic Algorithms (GAs) have demonstrated their efficiency on single and multiple criteria optimization. Additionally to their robustness, GAs can handle non-valid data which may appear during the optimization. Consequently GAs work on most general cases. A parallelized framework has been developed to reduce the time spent for optimizations and evaluation of large samples. A test has shown a good scaling efficiency of this parallelized framework. This coupling method has been applied to the case of SYCOMORE (System COde for MOdeling tokamak REactor) which is a system code developed in form of a modular workflow for designing magnetic fusion reactors. The coupling of SYCOMORE with the optimization platform URANIE enables design optimization along various figures of merit and constraints. (C) 2015 EURATOM. Published by Elsevier B.V. All rights reserved.
Luc Di Gallo, Cédric Reux, Frédéric Imbeaux, Jean-François Artaud, Michal Owsiak, et al.. Coupling between a multi-physics workflow engine and an optimization framework. Computer Physics Communications, Elsevier, 2016, 200, pp.76-86. <10.1016/j.cpc.2015.11.002>. <hal-01461783>
The goal of this work is to determine classes of traveling solitary wave solutions for Lattice Boltzmann schemes by means of an hyperbolic ansatz. It is shown that spurious solitary waves can occur in finite-difference solutions of nonlinear wave equation. The occurence of such a spurious solitary wave, which exhibits a very long life time, results in a non-vanishing numerical error for arbitrary time in unbounded numerical domain. Such a behavior is referred here to have a structural instability of the scheme, since the space of solutions spanned by the numerical scheme encompasses types of solutions (solitary waves in the present case) that are not solutions of the original continuous equations. This paper extends our previous work about classical schemes to Lattice Boltzmann schemes ([1], [2], [3],[4]).
Claire David, Pierre Sagaut. Structural stability of Lattice Boltzmann schemes. Physica A, Elsevier, 2016, 444, pp.1-8. <10.1016/j.physa.2015.09.089>. <hal-01298987>
J. Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, IOP Publishing, 2016, T167, . Plus de détails...
A thermal wall model is developed for the SolEdge2D-EIRENE edge transport code for calculating the surface temperature of the actively-cooled vessel components in interaction with the plasma. This is a first step towards a self-consistent evaluation of the recycling of particles, which depends on the wall surface temperature. The proposed thermal model is built to match both steady-state temperature and time constant of actively-cooled plasma facing components. A benchmark between this model and the Finite Element Modelling code CAST3M is performed in the case of an ITER-like monoblock. An example of application is presented for a SolEdge2D-EIRENE simulation of a medium-power discharge in the WEST tokamak, showing the steady-state wall temperature distribution and the temperature cycling due to an imposed Edge Localised Mode-like event.
J. Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, IOP Publishing, 2016, T167, <10.1088/0031-8949/T167/1/014073>. <hal-01459103>
Cai S-G., Ouahsine A., Julien Favier, Hoarau Y.. Improved Implicit Immersed Boundary Method via Operator Splitting, Computational Methods for Solids and Fluids. Multiscale Analysis, Probability Aspects and Model Reduction, Computational Methods in Applied Sciences, Springer, pp.49--66, 2016. Plus de détails...
Cai S-G., Ouahsine A., Julien Favier, Hoarau Y.. Improved Implicit Immersed Boundary Method via Operator Splitting, Computational Methods for Solids and Fluids. Multiscale Analysis, Probability Aspects and Model Reduction, Computational Methods in Applied Sciences, Springer, pp.49--66, 2016. <hal-01313518>
Benjamin Kadoch, Thorsten Reimann, Kai Schneider, Michael Schäfer. Comparison of a spectral method with volume penalization and a finite volume method with body fitted grids for turbulent flows. Computers and Fluids, Elsevier, 2016, 133, pp.140-150. Plus de détails...
We consider a turbulent flow past periodic hills at Reynolds number 1400 and compare two numerical methods: A Fourier pseudo–spectral scheme with volume penalization to model the no-slip boundary conditions and a finite volume method with body fitted grids. A detailed comparison of the results is presented for mean velocity profiles and Reynolds stress and confronted with those obtained by Breuer et al. [1]. In addition higher order statistics are performed and their scale-dependence is analyzed using orthogonal wavelets. Moreover, for the Fourier pseudo-spectral scheme, the influence of the Reynolds number is investigated.
Benjamin Kadoch, Thorsten Reimann, Kai Schneider, Michael Schäfer. Comparison of a spectral method with volume penalization and a finite volume method with body fitted grids for turbulent flows. Computers and Fluids, Elsevier, 2016, 133, pp.140-150. <10.1016/j.compfluid.2016.04.028>. <hal-01455110>
Shahram Khazaie, Régis Cottereau, D Clouteau. Influence of the spatial correlation structure of an elastic random medium on its scattering properties. Journal of Sound and Vibration, Elsevier, 2016, 370, pp.132-148. Plus de détails...
In the weakly heterogeneous regime of elastic wave propagation through a random medium, transport and diffusion models for the energy densities can be set up. In the isotropic case, the scattering cross sections are explicitly known as a function of the wave number and the correlations of the Lamé parameters and density. In this paper, we discuss the precise influence of the correlation structure on the scattering cross sections, mean free paths and diffusion parameter, and separate that influence from that of the correlation length and variance. We also analyze the convergence rates towards the low-and high-frequency ranges. For all analyses, we consider five different correlation structures, that allow us to explore a wide range of behaviors. We identify that the controlling factors for the low-frequency behavior are the value of the Power Spectral Density Function (PSDF) and its first non-vanishing derivative at the origin. In the high frequency range, the controlling factor is the third moment of the PSDF (which may be unbounded).
Shahram Khazaie, Régis Cottereau, D Clouteau. Influence of the spatial correlation structure of an elastic random medium on its scattering properties. Journal of Sound and Vibration, Elsevier, 2016, 370, pp.132-148. <10.1016/j.jsv.2016.01.012>. <hal-01281405>
Xun Wang, Zhongzhan Zhang, Shoumei Li. Set-valued and interval-valued stationary time series. Journal of Multivariate Analysis, Elsevier, 2016, 145, pp.208 - 223. Plus de détails...
Stationarity is a key tool in classical time series. In order to analyze the set-valued time series, it must be extended to the set-valued case. In this paper, stationary set-valued time series is defined via DpDp metric of set-valued random variables. Then, estimation methods of expectation and auto-covariance function of stationary set-valued time series are proposed. Unbiasedness and consistency of the expectation estimator and asymptotic unbiasedness of the auto-covariance function estimator are justified. After that, a special case of the set-valued time series, known as interval-valued time series, is considered. Two forecast methods of the stationary interval-valued time series are explicitly presented. Furthermore, the interval-valued time series is contextualized in the Box–Jenkins framework: an interval-valued autoregression model, along with its parameter estimation method, is introduced. Finally, experiments on both simulated and real data are presented to justify the efficiency of the parameters estimation method and the availability of the proposed model.
Xun Wang, Zhongzhan Zhang, Shoumei Li. Set-valued and interval-valued stationary time series. Journal of Multivariate Analysis, Elsevier, 2016, 145, pp.208 - 223. <10.1016/j.jmva.2015.12.010>. <hal-01450819>
Lyes Bordja, Emilia Arco, Éric Serre, Rachid Bessaih. EFFECTS OF AXIAL MAGNETIC FIELD AND THERMAL CONVECTION ON A COUNTERROTATING VON KARMAN FLOW. Heat Transfer Research, Begell House, 2016, 47 (5), pp.471-488. Plus de détails...
The effects of thermal convection and of a constant axial magnetic field on a von Karman flow driven by the exact counter-rotation of two lids are investigated in a vertical cylinder of aspect ratio Gamma(= height/radius) = 2 at a fixed Reynolds number Re(= Omega R-2/v) = 300. Direct numerical simulations are performed when varying separately the Rayleigh and Hartmann numbers in the range [0, 1800] and [0, 20], respectively, in the limit of the Boussinesq approximation and of a small magnetic Reynolds numbers, Re-m << 1. Without a magnetic field, the base flow symmetries of the von Karman flow are broken by thermal convection that becomes dominant in the range of Ra [500, 1000]. Three-dimensional solutions are characterized by the occurrence of a steady, m = 1, azimuthal mode exhibiting a cat's eye vortex in the circumferential plane. When increasing the Rayleigh number in the range [500, 1000], the vortex pulsates in an oscillatory manner, due to variations of the flow intensity. Otherwise, increasing the axial magnetic field intensity stabilizes the flow, and the oscillatory motion can be inhibited. Numerical solutions show that the critical Rayleigh number for transition increases linearly with the Hartmann number. Finally, results show that when varying the Rayleigh number, the structure of the electric potential can be strongly modified by thermal convection. Such an observation suggests new induction mechanisms in the case of small nonzero values of the magnetic Reynolds number.
Lyes Bordja, Emilia Arco, Éric Serre, Rachid Bessaih. EFFECTS OF AXIAL MAGNETIC FIELD AND THERMAL CONVECTION ON A COUNTERROTATING VON KARMAN FLOW. Heat Transfer Research, Begell House, 2016, 47 (5), pp.471-488. <10.1615/HeatTransRes.2016007441>. <hal-01462070>
S. Croquer, S. Poncet, Z. Aidoun. Turbulence modeling of a single-phase R134a supersonic ejector. Part 1: Numerical benchmark. International Journal of Refrigeration, Elsevier, 2016, 61 (8), pp.140-152. Plus de détails...
The present work reports a numerical analysis of a supersonic ejector in single-phase conditions using R134a as the working fluid. A numerical benchmark of some thermodynamic and two-equation turbulence models has been carried out to highlight the numerical model offering the best compromise between accuracy and calculation cost. The validation is achieved by comparing the predicted entrainment ratio with the experimental data of Garcia del Valle et al. (2014). The k−ω SST model together with the REFPROP 7.0 database equation appears to be the best combination to predict accurately the ejector performance and capture the shock wave structure. The influence of the outlet temperature, the discussion about the validity of some assumptions made by one-dimensional (1D) models and the exergy analysis within the ejector for the present operating conditions will later be discussed in Part 2 (Croquer et al., 2015).
S. Croquer, S. Poncet, Z. Aidoun. Turbulence modeling of a single-phase R134a supersonic ejector. Part 1: Numerical benchmark. International Journal of Refrigeration, Elsevier, 2016, 61 (8), pp.140-152. <10.1016/j.ijrefrig.2015.07.030>. <hal-01300110>
Frank G. Jacobitz, Kai Schneider, Wouter J. T. Bos, Marie Farge. Structure of sheared and rotating turbulence: Multiscale statistics of Lagrangian and Eulerian accelerations and passive scalar dynamics. Physical Review E , American Physical Society (APS), 2016, 93 (1), pp.013113. Plus de détails...
The acceleration statistics of sheared and rotating homogeneous turbulence are studied using direct numerical simulation results. The statistical properties of Lagrangian and Eulerian accelerations are considered together with the influence of the rotation to shear ratio, as well as the scale dependence of their statistics. The probability density functions (pdfs) of both Lagrangian and Eulerian accelerations show a strong and similar dependence on the rotation to shear ratio. The variance and flatness of both accelerations are analyzed and the extreme values of the Eulerian acceleration are observed to be above those of the Lagrangian acceleration. For strong rotation it is observed that flatness yields values close to three, corresponding to Gaussian-like behavior, and for moderate and vanishing rotation the flatness increases. Furthermore, the Lagrangian and Eulerian accelerations are shown to be strongly correlated for strong rotation due to a reduced nonlinear term in this case. A wavelet-based scale-dependent analysis shows that the flatness of both Eulerian and Lagrangian accelerations increases as scale decreases, which provides evidence for intermittent behavior. For strong rotation the Eulerian acceleration is even more intermittent than the Lagrangian acceleration, while the opposite result is obtained for moderate rotation. Moreover, the dynamics of a passive scalar with gradient production in the direction of the mean velocity gradient is analyzed and the influence of the rotation to shear ratio is studied. Concerning the concentration of a passive scalar spread by the flow, the pdf of its Eulerian time rate of change presents higher extreme values than those of its Lagrangian time rate of change. This suggests that the Eulerian time rate of change of scalar concentration is mainly due to advection, while its Lagrangian counterpart is only due to gradient production and viscous dissipation.
Frank G. Jacobitz, Kai Schneider, Wouter J. T. Bos, Marie Farge. Structure of sheared and rotating turbulence: Multiscale statistics of Lagrangian and Eulerian accelerations and passive scalar dynamics. Physical Review E , American Physical Society (APS), 2016, 93 (1), pp.013113. <10.1103/PhysRevE.93.013113>. <hal-01299256>
Zhe Li, Julien Favier, Umberto D 'Ortona, Sébastien Poncet. An immersed boundary-lattice Boltzmann method for single- and multi-component fluid flows. Journal of Computational Physics, Elsevier, 2016, 304, pp.424-440. Plus de détails...
The paper presents a numerical method to simulate single-and multi-component fluid flows around moving/deformable solid boundaries, based on the coupling of Immersed Boundary (IB) and Lattice Boltzmann (LB) methods. The fluid domain is simulated with LB method using the single relaxation time BGK model, in which an interparticle potential model is applied for multi-component fluid flows. The IB-related force is directly calculated with the interpolated definition of the fluid macroscopic velocity on the Lagrangian points that define the immersed solid boundary. The present IB-LB method can better ensure the no-slip solid boundary condition, thanks to an improved spreading operator. The proposed method is validated through several 2D/3D single-and multi-component fluid test cases with a particular emphasis on wetting conditions on solid wall. Finally, a 3D two-fluid application case is given to show the feasibility of modeling the fluid transport via a cluster of beating cilia.
Zhe Li, Julien Favier, Umberto D 'Ortona, Sébastien Poncet. An immersed boundary-lattice Boltzmann method for single- and multi-component fluid flows. Journal of Computational Physics, Elsevier, 2016, 304, pp.424-440. <10.1016/j.jcp.2015.10.026>. <hal-01225681>
Vincent Mons, Claude Cambon, Pierre Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically averaged descriptors. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2016, 788, pp.147- 182. Plus de détails...
A nonlinear spectral model in terms of spherically averaged descriptors is derived for the prediction of homogeneous turbulence dynamics in the presence of arbitrary mean-velocity gradients. The governing equations for the tensor R^ij(k,t), the Fourier transform of the two-point second-order correlation tensor, are first closed by an anisotropic eddy-damped quasinormal Markovian procedure. This closure is restricted to turbulent flows where linear effects induced by mean-flow gradients have no essential qualitative effects on the dynamics of triple correlations compared with the induced production effects in the equations for second-order correlations. Truncation at the first relevant order of spectral angular dependence allows us to derive from these equations in vector k our final model equations in terms of the wavenumber modulus k only. Analytical spherical integration results in a significant decrease in computational cost. Besides, the model remains consistent with the decomposition in terms of directional anisotropy and polarization anisotropy, with a spherically averaged anisotropic spectral tensor for each contribution. Restriction of anisotropy to spherically averaged descriptors, however, entails a loss of information, and realizability conditions are considered to quantify the upper boundary of anisotropy that can be investigated with the proposed model. Several flow configurations are considered to assess the validity of the present model. Satisfactory agreement with experiments on grid-generated turbulence subjected to successive plane strains is observed, which confirms the capability of the model to account for production of anisotropy by mean-flow gradients. The nonlinear transfer terms of the model are further tested by considering the return to isotropy (RTI) of different turbulent flows. Different RTI rates for directional anisotropy and polarization anisotropy allow us to correctly predict the apparent delayed RTI shown after axisymmetric expansion. The last test case deals with homogeneous turbulence subjected to a constant pure plane shear. The interplay between linear and nonlinear effects is reproduced, yielding the eventual exponential growth of the turbulent kinetic energy.
Vincent Mons, Claude Cambon, Pierre Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically averaged descriptors. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2016, 788, pp.147- 182. <10.1017/jfm.2015.705>. <hal-01298951>
Shahram Khazaie, Xun Wang, Pierre Sagaut. Localization of random acoustic sources in an inhomogeneous medium. Journal of Sound and Vibration, Elsevier, 2016, 384, pp.75 - 93. Plus de détails...
In this paper, the localization of a random sound source via different source localization methods is considered, the emphasis being put on the robustness and the accuracy of classical methods in the presence of uncertainties. The sound source position is described by a random variable and the sound propagation medium is assumed to have spatially varying parameters with known values. Two approaches are used for the source identification: time reversal and beamforming. The probability density functions of the random source position are estimated using both methods. The focal spot resolutions of the time reversal estimates are also evaluated. In the numerical simulations, two media with different correlation lengths are investigated to account for two different scattering regimes: one has a correlation length relatively larger than the wavelength and the other has a correlation length comparable to the wavelength. The results show that the required sound propagation time and source estimation robustness highly depend on the ratio between the correlation length and the wavelength. It is observed that source identification methods have different robustness in the presence of uncertainties. Advantages and weaknesses of each method are discussed.
Shahram Khazaie, Xun Wang, Pierre Sagaut. Localization of random acoustic sources in an inhomogeneous medium. Journal of Sound and Vibration, Elsevier, 2016, 384, pp.75 - 93. <10.1016/j.jsv.2016.08.004>. <hal-01375680>
Vincent Mons, Claude Cambon, Pierre Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically averaged descriptors. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2016, 788, pp.142-182. Plus de détails...
A nonlinear spectral model in terms of spherically averaged descriptors is derived for the prediction of homogeneous turbulence dynamics in the presence of arbitrary mean-velocity gradients. The governing equations for the tensor $\hat{R}_{ij}(\mathbf k,t)$, the Fourier transform of the two-point second-order correlation tensor, are first closed by an anisotropic eddy-damped quasinormal Markovian procedure. This closure is restricted to turbulent flows where linear effects induced by mean-flow gradients have no essential qualitative effects on the dynamics of triple correlations compared with the induced production effects in the equations for second-order correlations. Truncation at the first relevant order of spectral angular dependence allows us to derive from these equations in vector $\mathbf k$ our final model equations in terms of the wavenumber modulus $k$ only. Analytical spherical integration results in a significant decrease in computational cost. Besides, the model remains consistent with the decomposition in terms of directional anisotropy and polarization anisotropy, with a spherically averaged anisotropic spectral tensor for each contribution. Restriction of anisotropy to spherically averaged descriptors, however, entails a loss of information, and realizability conditions are considered to quantify the upper boundary of anisotropy that can be investigated with the proposed model. Several flow configurations are considered to assess the validity of the present model. Satisfactory agreement with experiments on grid-generated turbulence subjected to successive plane strains is observed, which confirms the capability of the model to account for production of anisotropy by mean-flow gradients. The nonlinear transfer terms of the model are further tested by considering the return to isotropy (RTI) of different turbulent flows. Different RTI rates for directional anisotropy and polarization anisotropy allow us to correctly predict the apparent delayed RTI shown after axisymmetric expansion. The last test case deals with homogeneous turbulence subjected to a constant pure plane shear. The interplay between linear and nonlinear effects is reproduced, yielding the eventual exponential growth of the turbulent kinetic energy.
Vincent Mons, Claude Cambon, Pierre Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically averaged descriptors. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2016, 788, pp.142-182. <10.1017/jfm.2015.705 >. <hal-01276637>
I. Thiagalingam, Pierre Sagaut. Pseudo-homogeneous 1D RANS radial model for heat transfer in tubular packed beds. International Journal of Heat and Fluid Flow, Elsevier, 2016, 62 (Part B), pp.258-272. Plus de détails...
A RANS zonal pseudo-homogeneous 1D radial heat transfer model is derived using an homogenization technique along with high-fidelity microscopic simulation to calibrate the model free parameters. Thus, it is brought to light the importance of the mechanical dispersion in the mixing process, the similarity between turbulent and dispersive dynamics, the existence of a near wall zone characterized by a channeling effect which is responsible for the thermal resistance over the zone. A linear law for the effective thermal conductivity is proposed to assess the heat transfer within the disrupted thermal boundary layer. The model showed its ability to estimate the effective conductivity and the temperature field in the radial direction with satisfaction. Very good agreements are also found in the near wall zone where the temperature gradients are the highest. The model well estimated also the value of the wall temperature and the wall heat transfer coefficient for an imposed heat flux at the wall.
I. Thiagalingam, Pierre Sagaut. Pseudo-homogeneous 1D RANS radial model for heat transfer in tubular packed beds. International Journal of Heat and Fluid Flow, Elsevier, 2016, 62 (Part B), pp.258-272. <10.1016/j.ijheatfluidflow.2016.10.005>. <hal-01400641>
Journal: International Journal of Heat and Fluid Flow
Dmitry Kolomenskiy, Jean-Christophe Nave, Kai Schneider. Adaptive gradient-augmented level set method with multiresolution error estimation. Journal of Scientific Computing, Springer Verlag, 2016, 66 (1), pp.116-140. Plus de détails...
A space–time adaptive scheme is presented for solving advection equations in two space dimensions. The gradient-augmented level set method using a semi-Lagrangian formulation with backward time integration is coupled with a point value multiresolution analysis using Hermite interpolation. Thus locally refined dyadic spatial grids are introduced which are efficiently implemented with dynamic quadtree data structures. For adaptive time integration, an embedded Runge–Kutta method is employed. The precision of the new fully adaptive method is analysed and speed up of CPU time and memory compression with respect to the uniform grid discretization are reported.
Dmitry Kolomenskiy, Jean-Christophe Nave, Kai Schneider. Adaptive gradient-augmented level set method with multiresolution error estimation. Journal of Scientific Computing, Springer Verlag, 2016, 66 (1), pp.116-140. <10.1007/s10915-015-0014-7>. <hal-01146954>
Julien Favier, A. Revell, A. Pinelli. Fluid Structure Interaction of Multiple Flapping Filaments Using Lattice Boltzmann and Immersed Boundary Methods, 133, Springer. Advances in Fluid-Structure Interaction, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 133, Springer, 2016. Plus de détails...
Julien Favier, A. Revell, A. Pinelli. Fluid Structure Interaction of Multiple Flapping Filaments Using Lattice Boltzmann and Immersed Boundary Methods, 133, Springer. Advances in Fluid-Structure Interaction, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 133, Springer, 2016. <hal-01313517>
T. Engels, D. Kolomenskiy, Kai Schneider, F.-O. Lehmann, J. Sesterhenn. Bumblebee Flight in Heavy Turbulence. Physical Review Letters, American Physical Society, 2016, 116 (2), pp.028103. . Plus de détails...
High-resolution numerical simulations of a tethered model bumblebee in forward flight are performed superimposing homogeneous isotropic turbulent fluctuations to the uniform inflow. Despite tremendous variation in turbulence intensity, between 17% and 99% with respect to the mean flow, we do not find significant changes in cycle-averaged aerodynamic forces, moments or flight power when averaged over realizations, compared to laminar inflow conditions. The variance of aerodynamic measures, however, significantly increases with increasing turbulence intensity, which may explain flight instabilities observed in freely flying bees.
T. Engels, D. Kolomenskiy, Kai Schneider, F.-O. Lehmann, J. Sesterhenn. Bumblebee Flight in Heavy Turbulence. Physical Review Letters, American Physical Society, 2016, 116 (2), pp.028103. <http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.028103>. <10.1103/PhysRevLett.116.028103>. <hal-01299332>
Ralf Deiterding, Margarete O. Domingues, Sonia M. Gomes, Kai Schneider. Comparison of adaptive multiresolution and adaptive mesh refinement applied to simulations of the compressible Euler equations. Journal of Plasma Physics, Cambridge University Press (CUP), 2015, 81 (06). Plus de détails...
We present a detailed comparison between two adaptive numerical approaches to solve partial differential equations (PDEs), adaptive multiresolution (MR) and adaptive mesh refinement (AMR). Both discretizations are based on finite volumes in space with second order shock-capturing, and explicit time integration either with or without local time-stepping. The two methods are benchmarked for the compressible Euler equations in Cartesian geometry. As test cases a 2D Riemann problem, Lax-Liu 6, and a 3D ellipsoidally expanding shock wave have been chosen. We compare and assess their computational efficiency in terms of CPU time and memory requirements. We evaluate the accuracy by comparing the results of the adaptive computations with those obtained with the corresponding FV scheme using a regular fine mesh. We find that both approaches yield similar trends for CPU time compression for increasing number of refinement levels. MR exhibits more efficient memory compression than AMR and shows slightly enhanced convergence; however, a larger absolute overhead is measured for the tested codes.
Ralf Deiterding, Margarete O. Domingues, Sonia M. Gomes, Kai Schneider. Comparison of adaptive multiresolution and adaptive mesh refinement applied to simulations of the compressible Euler equations. Journal of Plasma Physics, Cambridge University Press (CUP), 2015, 81 (06). <hal-01300098>
Yongliang Feng, Pierre Sagaut, Wenquan Tao. A three dimensional lattice model for thermal compressible flow on standard lattices. Journal of Computational Physics, Elsevier, 2015, 303, pp.514-529. Plus de détails...
A three-dimensional double distribution function thermal lattice Boltzmann model has been developed for simulation of thermal compressible flows in the low Mach number limit. Both the flow field and energy conservation equation are solved by LB approach. A higher order density distribution function on standard lattices is used to solve the flow field, while an energy distribution function is employed to compute the temperature field. The equation of state of thermal perfect gas is recovered by higher order Hermite polynomial expansions in Navier–Stokes–Fourier equations. The equilibrium distribution functions of D3Q15, D3Q19 and D3Q27 lattices are obtained from the Hermite expansion. They exhibit slight differences originating in differences in the discrete lattice symmetries. The correction terms in LB models for third order derivation are added using an external force in orthogonal polynomials form. Present models are successfully assessed considering several test cases, namely the thermal Couette flow, Rayleigh–Bénard convection, natural convection in square cavity and a spherical explosion in a 3D enclosed box. The numerical results are in good agreement with both analytical solution and results given by previous authors.
Yongliang Feng, Pierre Sagaut, Wenquan Tao. A three dimensional lattice model for thermal compressible flow on standard lattices. Journal of Computational Physics, Elsevier, 2015, 303, pp.514-529. <10.1016/j.jcp.2015.09.011>. <hal-01276507>
Xun Wang, Shahram Khazaie, Pierre Sagaut. Sound source localization in a randomly inhomogeneous medium using matched statistical moment method. Journal of the Acoustical Society of America, Acoustical Society of America, 2015, 138 (6), pp.3896. Plus de détails...
This paper investigates the problem of sound source localization from acoustical measurements obtained by an array of microphones. The sound propagation medium is assumed to be randomly inhomogeneous, being modelled by a random function of space. In this case, classical source localization methods (e.g., beamforming, near-field acoustical holography, and time reversal) cannot be used anymore. Therefore, an approach based on the statistical moments of acoustical measurement is proposed to solve the aforementioned problem. In this work, a Karhunen–Loève expansion is used so that the random medium can be represented by a small number of uncorrelated and identically distributed random variables. The statistical characteristics of the measurements in terms of probability density function and statistical moments are also studied. Then, the sound source is localized by minimizing the error of statistical moments between the real measurements obtained from the microphone array and the measurements simulated from an assumed source. Finally, a numerical example is introduced to justify the proposed method. This experiment shows that the random field can be replicated by a very small number of random variables, the statistical moments of measurements guarantee the convergence, and the source location can be accurately estimated using the proposed source localization method.
Xun Wang, Shahram Khazaie, Pierre Sagaut. Sound source localization in a randomly inhomogeneous medium using matched statistical moment method. Journal of the Acoustical Society of America, Acoustical Society of America, 2015, 138 (6), pp.3896. <10.1121/1.4938238>. <hal-01276517>
Journal: Journal of the Acoustical Society of America
Kai Schneider. Immersed boundary methods for numerical simulation of confined fluid and plasma turbulence in complex geometries: a review. Journal of Plasma Physics, Cambridge University Press (CUP), 2015, 81 (06), pp.435810601. Plus de détails...
Immersed boundary methods for computing confined fluid and plasma flows in complex geometries are reviewed. The mathematical principle of the volume penalization technique is described and simple examples for imposing Dirichlet and Neumann boundary conditions in one dimension are given. Applications for fluid and plasma turbulence in two and three space dimensions illustrate the applicability and the efficiency of the method in computing flows in complex geometries, for example in toroidal geometries with asymmetric poloidal cross-sections.
Kai Schneider. Immersed boundary methods for numerical simulation of confined fluid and plasma turbulence in complex geometries: a review. Journal of Plasma Physics, Cambridge University Press (CUP), 2015, 81 (06), pp.435810601. <10.1017/S0022377815000598>. <hal-01299254>
Marie Farge, Kai Schneider. Wavelet transforms and their applications to MHD and plasma turbulence: a review. Journal of Plasma Physics, Cambridge University Press (CUP), 2015, 81 (06), pp.435810602. Plus de détails...
Wavelet analysis and compression tools are reviewed and different applications to study MHD and plasma turbulence are presented. We introduce the continuous and the orthogonal wavelet transform and detail several statistical diagnostics based on the wavelet coefficients. We then show how to extract coherent structures out of fully developed turbulent flows using wavelet-based denoising. Finally some multiscale numerical simulation schemes using wavelets are described. Several examples for analyzing, compressing and computing one, two and three dimensional turbulent MHD or plasma flows are presented.
Marie Farge, Kai Schneider. Wavelet transforms and their applications to MHD and plasma turbulence: a review. Journal of Plasma Physics, Cambridge University Press (CUP), 2015, 81 (06), pp.435810602. <10.1017/S0022377815001075>. <hal-01299264>
Antoine Briard, Thomas Gomez, Pierre Sagaut, Souzan Memari. Passive scalar decay laws in isotropic turbulence: Prandtl number effects. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2015, 784, pp.274 - 303. Plus de détails...
The passive scalar dynamics in a freely decaying turbulent flow is studied. The classical framework of homogeneous isotropic turbulence without forcing is considered. Both low and high Reynolds number regimes are investigated for very small and very large Prandtl numbers. The long time behaviours of integrated quantities such as the scalar variance or the scalar dissipation rate are analyzed by considering that the decay follows power laws. This study addresses three major topics. Firstly, the Comte-Bellot and Corrsin (CBC) dimensional analysis for the temporal decay exponents is extended to the case of a passive scalar when the permanence of large eddies is broken. Secondly, using numerical simulations based on eddy-damped quasi-normal markovian (EDQNM) model, the time evolution of integrated quantities is accurately determined for a wide range of Reynolds and Prandtl numbers. These simulations show that, whatever the Reynolds and the Prandtl numbers are, the decay follows an algebraic law with an exponent very close to the value predicted by the CBC theory. Finally, the initial position of the scalar integral scale L T has no influence on the asymptotic values of the decay exponents, and an analytical law predicting the relative positions of the kinetic and scalar spectra peaks is derived.
Antoine Briard, Thomas Gomez, Pierre Sagaut, Souzan Memari. Passive scalar decay laws in isotropic turbulence: Prandtl number effects. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2015, 784, pp.274 - 303. <10.1017/jfm.2015.575>. <hal-01429641>
Romain Oguic, Stéphane Viazzo, Sébastien Poncet. A parallelized multidomain compact solver for incompressible turbulent flows in cylindrical geometries. Journal of Computational Physics, Elsevier, 2015, 300, pp.710-731. Plus de détails...
We present an efficient parallelized multidomain algorithm for solving the 3D Navier–Stokes equations in cylindrical geometries. The numerical method is based on fourth-order compact schemes in the two non-homogeneous directions and Fourier series expansion in the azimuthal direction. The temporal scheme is a second-order semi-implicit projection scheme leading to the solution of five Helmholtz/Poisson equations. To handle the singularity appearing at the axis in cylindrical coordinates, while being able to have a thinner or conversely a coarser mesh in this zone, parity conditions are imposed at r=0r=0 for each flow variable and azimuthal Fourier mode. To simulate flows in irregularly shaped cylindrical geometries and benefit from a hybrid OpenMP/MPI parallelization, an accurate perfectly free-divergence multidomain method based on the influence matrix technique is proposed. First, the accuracy of the present solver is checked by comparison with analytical solutions and the scalability is then evaluated. Simulations using the present code are then compared to reliable experimental and numerical results of the literature showing good quantitative agreements in the cases of the axisymmetric and 3D unsteady vortex breakdowns in a cylinder and turbulent pipe flow. Finally to show the capability of the algorithm to deal with more complex flows relevant of turbomachineries, the turbulent flow inside a simplified stage of High-Pressure compressor is considered.
Romain Oguic, Stéphane Viazzo, Sébastien Poncet. A parallelized multidomain compact solver for incompressible turbulent flows in cylindrical geometries. Journal of Computational Physics, Elsevier, 2015, 300, pp.710-731. <10.1016/j.jcp.2015.08.003>. <hal-01299082>
Amaury Bannier, Éric Garnier, Pierre Sagaut. Riblet Flow Model Based on an Extended FIK Identity. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2015, 95 (2-3), pp.351-376. Plus de détails...
Large Eddy Simulations of zero-pressure-gradient turbulent boundary layers over riblets have been conducted. All along the controlled domain, riblets maintain a significant 11 % drag reduction with respect to the flat plate at the same R e τ (from 250 to 450). To compare the flows above riblets and a reference smooth wall, an appropriate vertical shift between the two surfaces is required. In the present study, the “vertical origin” is set using the identity of Fukagata, Iwamoto and Kasagi (FIK) in Phys. Fluids, vol. 14, 2002, L73. This identity, which provides a physically meaningful decomposition of the skin friction, has been extended to complex wall surfaces and constitutes the basis for the derivation of a new virtual origin. Using this FIK-based origin, it is shown that the complex interactions between the riblets and the near-wall turbulent structures can be taken into account by a simple shift of the two axes of the mean and turbulent velocity profiles. The appropriate upward shift Δu +, typical for drag reduction, is directly dependent on the skin friction on the riblets and on the reference smooth plate at the same R e τ .
Amaury Bannier, Éric Garnier, Pierre Sagaut. Riblet Flow Model Based on an Extended FIK Identity. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2015, 95 (2-3), pp.351-376. <10.1007/s10494-015-9624-2>. <hal-01276488>
Anna Karina Fontes Gomes, Margarete Oliveira Domingues, Kai Schneider, Odim Mendes, Ralf Deiterding. An adaptive multiresolution method for ideal magnetohydrodynamics using divergence cleaning with parabolic–hyperbolic correction. Applied Numerical Analysis and Computational Mathematics, Wiley-VCH Verlag: No OnlineOpen, 2015, 95 (4), pp.199-213. Plus de détails...
We present an adaptive multiresolution method for the numerical simulation of ideal magnetohydrodynamics in two space dimensions. The discretization uses a finite volume scheme based on a Cartesian mesh and an explicit compact Runge–Kutta scheme for time integration. Harten's cell average multiresolution allows to introduce a locally refined spatial mesh while controlling the error. The incompressibility of the magnetic field is controlled by using a Generalized Lagrangian Multiplier (GLM) approach with a mixed hyperbolic–parabolic correction. Different applications to two-dimensional problems illustrate the properties of the method. For each application CPU time and memory savings are reported and numerical aspects of the method are discussed. The accuracy of the adaptive computations is assessed by comparison with reference solutions computed on a regular fine mesh.
Anna Karina Fontes Gomes, Margarete Oliveira Domingues, Kai Schneider, Odim Mendes, Ralf Deiterding. An adaptive multiresolution method for ideal magnetohydrodynamics using divergence cleaning with parabolic–hyperbolic correction. Applied Numerical Analysis and Computational Mathematics, Wiley-VCH Verlag: No OnlineOpen, 2015, 95 (4), pp.199-213. <10.1016/j.apnum.2015.01.007>. <hal-01299252>
Journal: Applied Numerical Analysis and Computational Mathematics
Dmitry Kolomenskiy, Romain Nguyen van Yen, Kai Schneider. Analysis and discretization of the volume penalized Laplace operator with Neumann boundary conditions. Applied Numerical Analysis and Computational Mathematics, Wiley-VCH Verlag: No OnlineOpen, 2015, 95, pp.238-249. Plus de détails...
We study the properties of an approximation of the Laplace operator with Neumann boundary conditions using volume penalization. For the one-dimensional Poisson equation we compute explicitly the exact solution of the penalized equation and quantify the penalization error. Numerical simulations using finite differences allow then to assess the discretization and penalization errors. The eigenvalue problem of the penalized Laplace operator with Neumann boundary conditions is also studied. As examples in two space dimensions, we consider a Poisson equation with Neumann boundary conditions in rectangular and circular domains.
Dmitry Kolomenskiy, Romain Nguyen van Yen, Kai Schneider. Analysis and discretization of the volume penalized Laplace operator with Neumann boundary conditions. Applied Numerical Analysis and Computational Mathematics, Wiley-VCH Verlag: No OnlineOpen, 2015, 95, pp.238-249. <10.1016/j.apnum.2014.02.003>. <hal-01299247>
Journal: Applied Numerical Analysis and Computational Mathematics
I. Thiagalingam, M. Dallet, I. Bennaceur, S. Cadalen, Pierre Sagaut. Exact non local expression for the wall heat transfer coefficient in tubular catalytic reactors. International Journal of Heat and Fluid Flow, Elsevier, 2015, 54, pp.97-106. Plus de détails...
A new exact and non local expression for the wall Nusselt number is derived to have a deep insight into the physical mechanisms that govern the wall heat transfer. 3D high-fidelity numerical simulations (RANS) are then carried out in tubular packed beds and a new set of criteria is defined to extend the Representative Elementary Volume concept to packed bed configurations which enables to unequivocally up-scale 3D simulation data to the observation scale. The mean flow deviation and the mechanical dispersion are shown to play a key role in the wall heat transfer. Finally, the usual correlations of the form View the MathML source Nu=αRepβ found in the literature for the Nusselt number are validated through fine 3D simulations and on the basis of physical investigations for 4000 ⩽ Rep ⩽ 30,000.
I. Thiagalingam, M. Dallet, I. Bennaceur, S. Cadalen, Pierre Sagaut. Exact non local expression for the wall heat transfer coefficient in tubular catalytic reactors. International Journal of Heat and Fluid Flow, Elsevier, 2015, 54, pp.97-106. <10.1016/j.ijheatfluidflow.2015.03.007>. <hal-01276484>
Journal: International Journal of Heat and Fluid Flow
Cédric Reux, Luc Di Gallo, Frédéric Imbeaux, Jean-François Artaud, P. Bernardi, et al.. DEMO reactor design using the new modular system code SYCOMORE. Nuclear Fusion, IOP Publishing, 2015, 55 (7), . Plus de détails...
A demonstration power plant (DEMO) will be the next step for fusion energy following ITER. Some of the key design questions can be addressed by simulations using system codes. System codes aim to model the whole plant with all its subsystems and identify the impact of their interactions on the design choices. The SYCOMORE code is a modular system code developed to address key questions relevant to tokamak fusion reactor design. SYCOMORE is being developed within the European Integrated Tokamak Modelling framework and provides a global view (technology and physics) of the plant. It includes modules to address plasma physics, divertor physics, breeding blankets, shield design, magnet design and the power balance of plant. The code is coupled to an optimization framework which allows one to specify figures of merit and constraints to obtain optimized designs. Examples of pulsed and steady-state DEMO designs obtained using SYCOMORE are presented. Sensitivity to design assumptions is also studied, showing that the operational domain around working points can be narrow for some cases.
Cédric Reux, Luc Di Gallo, Frédéric Imbeaux, Jean-François Artaud, P. Bernardi, et al.. DEMO reactor design using the new modular system code SYCOMORE. Nuclear Fusion, IOP Publishing, 2015, 55 (7), <10.1088/0029-5515/55/7/073011>. <hal-01462144>
Pierre Magnico. Ion transport dependence on the ion pairing/solvation competition in cation-exchange membranes. Journal of Membrane Science, Elsevier, 2015, 483, pp.112-127. Plus de détails...
Effect of ion-pairing on ion partitioning at equilibrium and on transport properties is studied by means of the Poisson–Nernst–Planck (PNP) equations. Owing to the low electrolyte solution relative permittivity (εSεS) and the high ion density in the membrane, the excess terms of the chemical potential must be computed. In this aim, the density functional theory and the binding mean sphere approximation were used in order to extend the PNP equations and to compute the association constant. The counter-ion/fixed-charge-group pairing and the counter-ion/co-ion one were examined. In the case of monovalent fixed charge, the total density of co-ion and the free one decreases with εSεS owing to the solvation contribution. So that it induces a decrease of the membrane system conductivity. If the counter-ion/co-ion pairing is considered, the free co-ion density and the conductivity increase when εSεS reaches small values. However in the ohmic regime, this dependence of the conductivity towards the free co-ion density is not always fulfilled.
Pierre Magnico. Ion transport dependence on the ion pairing/solvation competition in cation-exchange membranes. Journal of Membrane Science, Elsevier, 2015, 483, pp.112-127. <10.1016/j.memsci.2015.01.051>. <hal-01298876>
Wouter Bos, Benjamin Kadoch, Kai Schneider. Angular statistics of Lagrangian trajectories in turbulence. Physical Review Letters, American Physical Society, 2015, 114, pp.214502. Plus de détails...
The angle between subsequent particle displacement increments is evaluated as a function of the timelag in isotropic turbulence. It is shown that the evolution of this angle contains two well-defined power-laws, reflecting the multi-scale dynamics of high-Reynolds number turbulence. The proba-bility density function of the directional change is shown to be self-similar and well approximated by an analytically derived model assuming Gaussianity and independence of the velocity and the Lagrangian acceleration.
Wouter Bos, Benjamin Kadoch, Kai Schneider. Angular statistics of Lagrangian trajectories in turbulence. Physical Review Letters, American Physical Society, 2015, 114, pp.214502. <10.1103/PhysRevLett.114.214502>. <hal-01085070>
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, IOP Publishing, 2015, 57 (5), pp.054014. Plus de détails...
The 3D global edge turbulence code TOKAM3X is used to study the properties of edge particle turbulent transport in circular limited plasmas, including both closed and open flux surfaces. Turbulence is driven by an incoming particle flux from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed. Simulations show the existence of a complex self-organization of turbulence transport coupling scales ranging from a few Larmor radii up to the machine scale. Particle transport is largely dominated by small scale turbulence with fluctuations forming quasi field-aligned filaments. Radial particle transport is intermittent and associated with the propagation of coherent structures on long distances via avalanches. Long range correlations are also found in the poloidal and toroidal direction. The statistical properties of fluctuations vary with the radial and poloidal directions, with larger fluctuation levels and intermittency found in the outboard scrape-off layer (SOL). Radial turbulent transport is strongly ballooned, with 90% of the flux at the separatrix flowing through the low-field side. One of the main consequences is the existence of quasi-sonic asymmetric parallel flows driving a net rotation of the plasma. Simulations also show the spontaneous onset of an intermittent E × B rotation characterized by a larger shear at the separatrix. Strong correlation is found between the turbulent particle flux and the E × B flow shear in a phenomenology reminiscent of H-mode physics. The poloidal position of the limiter is a key player in the observed dynamics.
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, IOP Publishing, 2015, 57 (5), pp.054014. <10.1088/0741-3335/57/5/054014>. <hal-01299732>
Jorge A. Morales, Wouter J.T. Bos, Kai Schneider, David C. Montgomery. Magnetohydrodynamically generated velocities in confined plasma. Physics of Plasmas, American Institute of Physics, 2015, 22 (4), pp.042515. Plus de détails...
We investigate by numerical simulation the rotational flows in a toroid confining a conducting magnetofluid in which a current is driven by the application of externally supported electric and magnetic fields. The computation involves no microscopic instabilities and is purely magnetohydrodynamic (MHD). We show how the properties and intensity of the rotations are regulated by dimensionless numbers (Lundquist and viscous Lundquist) that contain the resistivity and viscosity of the magnetofluid. At the magnetohydrodynamic level (uniform mass density and incompressible magnetofluids), rotational flows appear in toroidal, driven MHD. The evolution of these flows with the transport coefficients, geometry, and safety factor are described.
Jorge A. Morales, Wouter J.T. Bos, Kai Schneider, David C. Montgomery. Magnetohydrodynamically generated velocities in confined plasma. Physics of Plasmas, American Institute of Physics, 2015, 22 (4), pp.042515. <10.1063/1.4918774>. <hal-00849742>
Olivier Roussel, Kai Schneider. Adaptive multiresolution computations applied to detonations. Zeitschrift für Physikalische Chemie, Oldenbourg Verlag, 2015, 229 (6), pp.931-953. Plus de détails...
A space-time adaptive method is presented for the reactive Euler equations describing chemically reacting gas flow where a two species model is used for the chemistry. The governing equations are discretized with a finite volume method and dynamic space adaptivity is introduced using multiresolution analysis. A time splitting method of Strang is applied to be able to consider stiff problems while keeping the method explicit. For time adaptivity an improved Runge--Kutta--Fehlberg scheme is used. Applications deal with detonation problems in one and two space dimensions. A comparison of the adaptive scheme with reference computations on a regular grid allow to assess the accuracy and the computational efficiency, in terms of CPU time and memory requirements.
Olivier Roussel, Kai Schneider. Adaptive multiresolution computations applied to detonations. Zeitschrift für Physikalische Chemie, Oldenbourg Verlag, 2015, 229 (6), pp.931-953. <hal-01118153>
Seyed Amin Ghaffari, Stéphane Viazzo, Kai Schneider, Patrick Bontoux. Simulation of forced deformable bodies interacting with two-dimensional incompressible flows: Application to fish-like swimming. International Journal of Heat and Fluid Flow, Elsevier, 2015, Theme special issue celebrating the 75th birthdays of Brian Launder and Kemo Hanjalic, 51, pp.88-109. Plus de détails...
We present an efficient algorithm for simulation of deformable bodies interacting with two-dimensional incompressible flows. The temporal and spatial discretizations of the Navier-Stokes equations in vorticity stream-function formulation are based on classical fourth-order Runge-Kutta and compact finite differences, respectively. Using a uniform Cartesian grid we benefit from the advantage of a new fourth-order direct solver for the Poisson equation to ensure the incompressibility constraint down to machine zero. For introducing a deformable body in fluid flow, the volume penalization method is used. A Lagrangian structured grid with prescribed motion covers the deformable body interacting with the surrounding fluid due to the hydrodynamic forces and moment calculated on the Eulerian reference grid. An efficient law for curvature control of an anguilliform fish, swimming to a prescribed goal, is proposed. Validation of the developed method shows the efficiency and expected accuracy of the algorithm for fish-like swimming and also for a variety of fluid/solid interaction problems.
Seyed Amin Ghaffari, Stéphane Viazzo, Kai Schneider, Patrick Bontoux. Simulation of forced deformable bodies interacting with two-dimensional incompressible flows: Application to fish-like swimming. International Journal of Heat and Fluid Flow, Elsevier, 2015, Theme special issue celebrating the 75th birthdays of Brian Launder and Kemo Hanjalic, 51, pp.88-109. <10.1016/j.ijheatfluidflow.2014.10.023>. <hal-00967077v2>
Journal: International Journal of Heat and Fluid Flow
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. Suction/Injection Effects on the Swirling Flow of a Reiner-Rivlin Fluid near a Rough Surface. Hindawi Publishing Corporation, 2015, 2015, Article ID 253504, 5 p. . Plus de détails...
The similarity equations for the Bödewadt flow of a non-Newtonian Reiner-Rivlin fluid, subject to uniform suction/injection, are solved numerically. The conventional no-slip boundary conditions are replaced by corresponding partial slip boundary conditions, owing to the roughness of the infinite stationary disk. The combined effects of surface slip, suction/injection velocity, and cross-viscous parameter on the momentum boundary layer are studied in detail. It is interesting to find that suction dominates the oscillations in the velocity profiles and decreases the boundary layer thickness significantly. On the other hand, injection has opposite effects on the velocity profiles and the boundary layer thickness.
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. Suction/Injection Effects on the Swirling Flow of a Reiner-Rivlin Fluid near a Rough Surface. Hindawi Publishing Corporation, 2015, 2015, Article ID 253504, 5 p. <http://www.hindawi.com/journals/fluids/2015/253504/>. <10.1155/2015/253504>. <hal-01100098>
Julien Favier, Alistair Revell, Alfredo Pinelli. Numerical study of flapping filaments in a uniform fluid flow. Journal of Fluids and Structures, Elsevier, 2015, 53, pp.26-35. Plus de détails...
The coupled dynamics of multiple flexible filaments (also called monodimen-sional flags) flapping in a uniform fluid flow is studied numerically for the cases of a side-by-side arrangement, and an in-line configuration. The modal behaviour and hydrodynamical properties of the sets of filaments are studied using a Lattice Boltzmann-Immersed Boundary method. The fluid momentum equations are solved on a Cartesian uniform lattice while the beating filaments are tracked through a series of markers, whose dynamics are functions of the forces exerted by the fluid, the filaments flexural rigidity and the tension. The instantaneous wall conditions on the filaments are imposed via a system of singular body forces, consistently discretised on the lattice of the Boltzmann equation. The results exhibits several flapping modes for two and three filaments placed side-by-side and are compared with experimental and theoretical studies. The hydrodynamical drafting, observed so far only experimentally on configurations of in-line flexible bodies, is also revisited numerically in this work, and the associated physical mechanism is identified. In certain geometrical and structural configuration, it is found that the upstream body experiences a reduced drag compared to the downstream body, which is the contrary of what is encountered on rigid bodies (cars, bicycles).
Julien Favier, Alistair Revell, Alfredo Pinelli. Numerical study of flapping filaments in a uniform fluid flow. Journal of Fluids and Structures, Elsevier, 2015, 53, pp.26-35. <10.1016/j.jfluidstructs.2014.11.010>. <hal-01118360>
Pedro Valero-Lara, Francisco D. Igual, Manuel Prieto-Matías, Alfredo Pinelli, Julien Favier. Accelerating fluid–solid simulations (Lattice-Boltzmann & Immersed-Boundary) on heterogeneous architectures. Journal of Computational Science, Elsevier, 2015, 10, pp.249-261. Plus de détails...
We propose a numerical approach based on the Lattice-Boltzmann (LBM) and Immersed Boundary (IB) methods to tackle the problem of the interaction of solids with an incompressible fluid flow, and its implementation on heterogeneous platforms based on data-parallel accelerators such as NVIDIA GPUs and the Intel Xeon Phi. We explain in detail the parallelization of these methods and describe a number of optimizations, mainly focusing on improving memory management and reducing the cost of host-accelerator communication. As previous research has consistently shown, pure LBM simulations are able to achieve good performance results on heterogeneous systems thanks to the high parallel efficiency of this method. Unfortunately, when coupling LBM and IB methods, the overheads of IB degrade the overall performance. As an alternative, we have explored different hybrid implementations that effectively hide such overheads and allow us to exploit both the multi-core and the hardware accelerator in a cooperative way, with excellent performance results.
Pedro Valero-Lara, Francisco D. Igual, Manuel Prieto-Matías, Alfredo Pinelli, Julien Favier. Accelerating fluid–solid simulations (Lattice-Boltzmann & Immersed-Boundary) on heterogeneous architectures. Journal of Computational Science, Elsevier, 2015, 10, pp.249-261. <10.1016/j.jocs.2015.07.002>. <hal-01225734>
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. EFFECTS OF SLIP ON THE VON KÁRMÁN SWIRLING FLOW AND HEAT TRANSFER IN A POROUS MEDIUM. Transactions of the Canadian Society for Mechanical Engineering, Canadian Society for Mechanical Engineering, 2015, 39 (2), pp.357-366. Plus de détails...
Numerical solutions are obtained for the fully coupled and highly nonlinear system of differential equations, arising due to the steady Kármán flow and heat transfer of a viscous fluid in a porous medium. The conven- tional no-slip boundary conditions are replaced by partial slip boundary conditions owing to the roughness of the disk surface. Combined effects of the slip λ and porosity γ parameters on the momentum and thermal boundary layers are studied in detail. Both parameters produce the same effects on the mean velocity pro- files, such that all velocity components are reduced by increasing either λ or γ. The temperature slip factor β has a dominating influence on the temperature profiles by decreasing the fluid temperature in the whole domain. The porosity parameter strongly decreases the heat transfer coefficient at the wall for low values of β and tends to an asymptotical limit around 0.1 for β 10. The porosity parameter γ increases the moment coefficient at the disk surface, which is found to monotonically decrease with λ .
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. EFFECTS OF SLIP ON THE VON KÁRMÁN SWIRLING FLOW AND HEAT TRANSFER IN A POROUS MEDIUM. Transactions of the Canadian Society for Mechanical Engineering, Canadian Society for Mechanical Engineering, 2015, 39 (2), pp.357-366. <hal-01300117>
Journal: Transactions of the Canadian Society for Mechanical Engineering
S-G Cai, A Ouahsine, H Smaoui, Julien Favier, Y Hoarau. An efficient implicit direct forcing immersed boundary method for incompressible flows. Journal of Physics: Conference Series, IOP Publishing, 2015, 574 (012165), pp.5. Plus de détails...
A novel efficient implicit direct forcing immersed boundary method for incompressible flows with complex boundaries is presented. In the previous work [1], the calculation is performed on the Cartesian grid regardless of the immersed object, with a fictitious force evaluated on the Lagrangian points to mimic the presence of the physical boundaries. However the explicit direct forcing method [1] fails to accurately impose the non-slip boundary condition on the immersed interface. In the present work, the calculation is based on the implicit treatment of the artificial force while in an effective way of system iteration. The accuracy is also improved by solving the Navier-Stokes equation with the rotational incremental pressure- correction projection method of Guermond and Shen [2]. Numerical simulations performed with the proposed method are in good agreement with those in the literature.
S-G Cai, A Ouahsine, H Smaoui, Julien Favier, Y Hoarau. An efficient implicit direct forcing immersed boundary method for incompressible flows. Journal of Physics: Conference Series, IOP Publishing, 2015, 574 (012165), pp.5. <10.1088/1742-6596/574/1/012165>. <hal-01225703>
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.420-423. Plus de détails...
The influence of the plasma facing components material on the scrape-off layer plasma is investigated. In particular, the energy recycling is found to be more pronounced for tungsten wall compared with carbon wall. Edge plasma simulations performed with the transport code SOLEDGE2D-EIRENE show that this enhanced energy recycling in the tungsten case leads to an increase of the scrape-off layer temperature. Moreover, the energy recycling depends on the ion angle of incidence with the wall. A PIC code has been used to model the ion acceleration in the magnetic pre-sheath and determine the later angle of incidence. These simulations show that ions mostly impact the wall with rather shallow incident angles leading to a further increase of the energy recycling.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.420-423. <10.1016/j.jnucmat.2014.09.061>. <hal-01225205>
Richard Howard, Eric Serre. Large-eddy simulation in a mixing tee junction: High-order turbulentstatistics analysis. International Journal of Heat and Fluid Flow, Elsevier, 2015, 51, pp.65-77. Plus de détails...
This study analyses the mixing and thermal fluctuations induced in a mixing tee junction with circular cross-sections when cold water flowing in a pipe is joined by hot water from a branch pipe. This config- uration is representative of industrial piping systems in which temperature fluctuations in the fluid may cause thermal fatigue damage on the walls. Implicit large-eddy simulations (LES) are performed for equal inflow rates corresponding to a bulk Reynolds number Re= 39,080. Two different thermal boundary conditions are studied for the pipe walls; an insulating adiabatic boundary and a conducting steel wall boundary. The predicted flow structures show a satisfactory agreement with the literature. The velocity and thermal fields (including high-order statistics) are not affected by the heat transfer with the steel walls. However, predicted thermal fluctuations at the boundary are not the same between the flow and the solid, showing that solid thermal fluctuations cannot be predicted by the knowledge of the fluid thermal fluctuations alone. The analysis of high-order turbulent statistics provides a better understand- ing of the turbulence features. In particular, the budgets of the turbulent kinetic energy and temperature variance allows a comparative analysis of dissipation, production and transport terms. It is found that the turbulent transport term is an important term that acts to balance the production. We therefore use a priori tests to evaluate three different models for the triple correlation
Richard Howard, Eric Serre. Large-eddy simulation in a mixing tee junction: High-order turbulentstatistics analysis. International Journal of Heat and Fluid Flow, Elsevier, 2015, 51, pp.65-77. <hal-01138803>
Journal: International Journal of Heat and Fluid Flow
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, IOP Publishing, 2015, 55 (5), pp.053025. Plus de détails...
In the perspective of operating tungsten monoblocks in WEST, the ongoing major upgrade of the Tore Supra tokamak, a dedicated modelling effort has been carried out to simulate the interaction between the edge plasma and the tungsten wall. A new transport code, SolEdge2D–EIRENE, has been developed with the ability to simulate the plasma up to the first wall. This is especially important for steady state operation, where thermal loads on all the plasma facing components, even remote from the plasma, are of interest. Moreover, main chamber tungsten sources are thought to dominate the contamination of the plasma core. We present here in particular new developments aimed at improving the description of the interface between the plasma and the wall, namely a way to treat sheath physics in a more faithful way using the output of 1D particle in cell simulations. Moreover, different models for prompt redeposition have been implemented and are compared. The latter is shown to play an important role in the balance between divertor and main chamber sources.
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, IOP Publishing, 2015, 55 (5), pp.053025. <hal-01225195>
Braza M., Bontoux P.. Synthesis on the activities of SIG36 Swirling Flows concerning rotation effects. M. Marek. ERCOFTAC Bulletin, 98, pp.3, 2015. Plus de détails...
Braza M., Bontoux P.. Synthesis on the activities of SIG36 Swirling Flows concerning rotation effects. M. Marek. ERCOFTAC Bulletin, 98, pp.3, 2015. <hal-01313520>
Ait-Moussa Nabila, Sébastien Poncet, Ghezal Abdelrahmane. Numerical Simulations of Co- and Counter-Taylor-Couette Flows: Influence of the Cavity Radius Ratio on the Appearance of Taylor Vortices. American Journal of Fluid Dynamics, http://www.sapub.org/journal/aimsandscope.aspx?journalid=1090, 2015, 5 (1), pp.17-22. Plus de détails...
Taylor-Couette flows in the annular region between rotating concentric cylinders are studied numerically to determine the combined effects of the co - and counter-rotation of the outer cylinder and the radius ratio on the system response. The computational procedure is based on a finite volume method using staggered grids. The axisymmetric conservative governing equations are solved using the SIMPLER algorithm. One considers the flow confined in a finite cavity with radius ratios η = 0.25, 0.5, 0.8 and 0.97. One has determined the critical points and properties for the bifurcation from the basic circular Couette flow (CCF) to the Taylor Vortex Flow (TVF) state. Indeed, the results are presented in terms of the critical Reynolds number Rei of the inner cylinder that depends on the rotational Reynolds number of the outer cylinder Reo andη. To show the capability of the present code, excellent quantitative agreement has been obtained between the calculations and previous experimental measurements for a wide range of radius ratios and rotation rates.
Ait-Moussa Nabila, Sébastien Poncet, Ghezal Abdelrahmane. Numerical Simulations of Co- and Counter-Taylor-Couette Flows: Influence of the Cavity Radius Ratio on the Appearance of Taylor Vortices. American Journal of Fluid Dynamics, http://www.sapub.org/journal/aimsandscope.aspx?journalid=1090, 2015, 5 (1), pp.17-22. <10.5923/j.ajfd.20150501.02>. <hal-01300130>
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.489-492. Plus de détails...
To understand the mechanisms behind poloidal asymmetries of the transport in the edge and SOL plasma, it is important to take into account drift velocity in the transport model. We investigate the effects of an imposed radial electric field on the plasma equilibrium in the transport code SOLEDGE2D. In the edge, we show an important modification of the flow pattern due to poloidal E × B drift velocity. The drift velocity generates asymmetry of the density through the Pfirsch–Schluter flows which creates an important parallel rotation through the viscous balance. In comparison to heat load imbalance studies in the SOL of divertor tokamak, a strong link between the amplitude of the radial electric field and the heat load imbalance in the SOL of limiter tokamak has been highlighted using different amplitude of the imposed radial electric field.
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.489-492. <10.1016/j.jnucmat.2014.10.079>. <hal-01225211>
Christophe Friess, R. Manceau, T.B. Gatski. Toward an equivalence criterion for Hybrid RANS/LES methods. Computers and Fluids, Elsevier, 2015, 122, pp.233-246. Plus de détails...
A criterion is established to assess the equivalence between hybrid RANS/LES methods, called H-equivalence, based on the modeled energy of the unresolved scales, which leads to similar low-order statistics of the resolved motion. Different equilibrium conditions are considered, and perturbation analyses about the equilibrium states are performed. The procedure is applied to demonstrate the equivalence between two particular hybrid methods, and leads to relationships between hybrid method parameters that control the partitioning of energy between the resolved and unresolved scales of motion. This equivalence is validated by numerical results obtained for the cases of plane and periodically constricted channel flows. This concept of H-equivalence makes it possible to view different hybrid methods as models for the same system of equations: as a consequence, detached-eddy simulation (DES), which is shown to be H-equivalent to the temporal partially integrated transport model (T-PITM) in inhomogeneous, stationary situations, can be interpreted as a model for the subfilter stress involved in the temporally filtered Navier–Stokes equations.
Christophe Friess, R. Manceau, T.B. Gatski. Toward an equivalence criterion for Hybrid RANS/LES methods. Computers and Fluids, Elsevier, 2015, 122, pp.233-246. <10.1016/j.compfluid.2015.08.010>. <hal-01246130>
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.654-658. Plus de détails...
A 3D global turbulence fluid code, TOKAM3X is used to investigate the effect of the limiter position on the edge plasma parallel flows and density profiles. Six configurations with different poloidal contact points in the machine are considered. For each one, asymmetric quasi-sonic parallel flows are found, owing to the ballooning of radial turbulent transport around the LFS mid-plane. In spite of the relative simplicity of the model used (isothermal, sheat-limited, no recycling), simulations exhibit trends in-line with experimental findings. Reversal of the flows is found when the limiter is moved from −30° under to 30° above the outboard mid-plane. The SOL width varies with the poloidal location and depends notably on the poloidal position of the limiter. Turbulence itself is shown to be impacted by the position of the limiter, radial transport appearing less ballooned with a LFS limiter than with a HFS.
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.654-658. <10.1016/j.jnucmat.2015.01.019>. <hal-01225200>
Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Jörn Sesterhenn. Numerical simulation of fluid–structure interaction with the volume penalization method. Journal of Computational Physics, Elsevier, 2015, 281, pp.96-115. Plus de détails...
We present a novel scheme for the numerical simulation of fluid–structure interaction problems. It extends the volume penalization method, a member of the family of immersed boundary methods, to take into account flexible obstacles. We show how the introduction of a smoothing layer, physically interpreted as surface roughness, allows for arbitrary motion of the deformable obstacle. The approach is carefully validated and good agreement with various results in the literature is found. A simple one-dimensional solid model is derived, capable of modeling arbitrarily large deformations and imposed motion at the leading edge, as it is required for the simulation of simplified models for insect flight. The model error is shown to be small, while the one-dimensional character of the model features a reasonably easy implementation. The coupled fluid–solid interaction solver is shown not to introduce artificial energy in the numerical coupling, and validated using a widely used benchmark. We conclude with the application of our method to models for insect flight and study the propulsive efficiency of one and two wing sections.
Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Jörn Sesterhenn. Numerical simulation of fluid–structure interaction with the volume penalization method. Journal of Computational Physics, Elsevier, 2015, 281, pp.96-115. <10.1016/j.jcp.2014.10.005>. <hal-01299253>
Francisco Toja-Silva, Julien Favier, Alfredo Pinelli. Radial Basis Function (RBF)-based Interpolation and Spreading for the Immersed Boundary Method. Computers and Fluids, Elsevier, 2014, 105, pp.66-75. Plus de détails...
Immersed boundary methods are efficient tools of growing interest as they allow to use generic CFD codes to deal with complex, moving and deformable geometries, for a reasonable computational cost compared to classical body- conformal or unstructured mesh approaches. In this work, we propose a new immersed boundary method based on a radial basis functions frame- work for the spreading-interpolation procedure. The radial basis function approach allows for dealing with a cloud of scattered nodes around the im- mersed boundary, thus enabling the application of the devised algorithm to any underlying mesh system. The proposed method can also keep into ac- count both Dirichlet and Neumann type conditions. To demonstrate the capabilities of our novel approach, the imposition of Dirichlet boundary con- ditions on a 2D cylinder geometry in a Navier-Stokes CFD solver, and the imposition of Neumann boundary conditions on an adiabatic wall in an un- steady heat conduction problem are considered. One of the most significant advantage of the proposed method lies in its simplicity given by the algo- rithmic possibility of carrying out the interpolation and spreading steps all together, in a single step.
Francisco Toja-Silva, Julien Favier, Alfredo Pinelli. Radial Basis Function (RBF)-based Interpolation and Spreading for the Immersed Boundary Method. Computers and Fluids, Elsevier, 2014, 105, pp.66-75. <10.1016/j.compfluid.2014.09.026>. <hal-01069809>
H Guillard, M Bilanceri, C Colin, Philippe Ghendrih, G Giorgiani, et al.. Parallel Kelvin-Helmholtz instability in edge plasma. Journal of Physics: Conference Series, IOP Publishing, 2014, Joint Varenna-Lausanne International Workshop 2014, 561, pp.012009. Plus de détails...
In the scrape-off layer (SOL) of tokamaks, the flow acceleration due to the presence of limiter or divertor plates rises the plasma velocity in a sonic regime. These high velocities imply the presence of a strong shear between the SOL and the core of the plasma that can possibly trigger some parallel shear flow instability. The existence of these instabilities, denoted as parallel Kelvin-Helmholtz instability in some works [1, 2] have been investigated theoretically in [3] using a minimal model of electrostatic turbulence composed of a mass density and parallel velocity equations. This work showed that the edge plasma around limiters might indeed be unstable to this type of parallel shear flow instabilities. In this work, we perform 3D simulations of the same simple mathematical model to validate an original finite volume numerical method aimed to the numerical study of edge plasma. This method combines the use of triangular unstructured meshes in the poloidal section and structured meshes in the toroidal direction and is particularly suited to the representation of the real complex geometry of the vacuum chamber of a tokamak. The numerical results confirm that in agreement with the theoretical expectations as well as with other numerical methods, the sheared flows in the SOL are subject to parallel Kelvin-Helmholtz instabilities. However, the growth rate of these instabilities is low and these computations require both a sufficient spatial resolution and a long simulation time. This makes the simulation of parallel Kelvin-Helmholtz instabilities a demanding benchmark.
H Guillard, M Bilanceri, C Colin, Philippe Ghendrih, G Giorgiani, et al.. Parallel Kelvin-Helmholtz instability in edge plasma. Journal of Physics: Conference Series, IOP Publishing, 2014, Joint Varenna-Lausanne International Workshop 2014, 561, pp.012009. <10.1088/1742-6596/561/1/012009>. <hal-01100365>
The dynamics of a magnetically forced conducting fluid in confined geometries is studied. A pseudospectral method with volume penalisation is used to solve the resistive magnetohydrodynamic (MHD) equations. A helical magnetic field is imposed via boundary conditions, which generates a response in the velocity field for large enough magnitudes. Different helical structures are observed in the flow depending on the magnitude and direction of the forcing and the cross-sectional geometry of the fluid domain. A computational technique for finding a solenoidal vector field which can be used in complex geometries is also proposed.
Sébastien Poncet, Stéphane Viazzo, Oguic Romain. Large eddy simulations of Taylor-Couette-Poiseuille flows in a narrow-gap system. Physics of Fluids, American Institute of Physics, 2014, 26 (10), pp.105108. . Plus de détails...
The present paper concerns Large-Eddy Simulations (LES) of turbulent Taylor-Couette-Poiseuille flows in a narrow-gap cavity for six different combinations of rotational and axial Reynolds numbers. The in-house numerical code has been first validated in a middle-gap cavity. Two sets of refined LES results, using the Wall-Adapting Local EddyViscosity(WALE) and theDynamic Smagorinsky subgrid-scale models availablewithin an in-house code based on high-order compact schemes, have been then compared with no noticeable difference on the mean flow field and theturbulent statistics. The WALE model enabling a saving of about 12% of computational effort has been finally used to investigate the influence on the hydrodynamics of the swirl parameter N within the range [1.49 − 6.71]. The swirl parameter N, which compares the effects of rotation of the inner cylinder and the axial flowrate, does not influence significantly the mean velocity profiles. Turbulence intensities are enhanced with increasing values of N with remarkably high peak values within the boundary layers. The inner rotating cylinder has a destabilizing effect inducing asymmetric profiles of the Reynolds stress tensor components. The rotor and stator boundary layers exhibit the main characteristics of two-dimensional boundary layers.Turbulence is also mainly at two-component there. Thin coherent structures appearing as negative (resp. positive) spiral rolls are observed along the rotor (resp. stator) side. Their inclination angle depends strongly on the value of the swirl parameter, which fixes the intensity of the crossflow. On the other hand, the intensity and the size of the coherent structures observed within the boundary layers are governed by the effective Reynolds number. For its highest value, they penetrate the whole gap. Finally, the results have been extended to the non-isothermal case in the forced convection regime. A correlation for the Nusselt number along the rotor has been provided showing a much larger dependence on the axial Reynolds number thanexpected from previous published works, while it depends classically on the Taylor number to the power 0.145 and on the Prandtl number to the power 0.3.
Sébastien Poncet, Stéphane Viazzo, Oguic Romain. Large eddy simulations of Taylor-Couette-Poiseuille flows in a narrow-gap system. Physics of Fluids, American Institute of Physics, 2014, 26 (10), pp.105108. <http://dx.doi.org/10.1063/1.4899196>. <10.1063/1.4899196>. <hal-01083052>
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak ă with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. Plus de détails...
To properly address turbulent transport in the edge plasma region of a ă tokamak, it is mandatory to describe the particle and heat outflow on ă wall components, using an accurate representation of the wall geometry. ă This is challenging for many plasma transport codes, which use a ă structured mesh with one coordinate aligned with magnetic surfaces. We ă propose here a penalization technique that allows modeling of particle ă and heat transport using such structured mesh, while also accounting for ă geometrically complex plasma-facing components. Solid obstacles are ă considered as particle and momentum sinks whereas ionic and electronic ă temperature gradients are imposed on both sides of the obstacles along ă the magnetic field direction using delta functions (Dirac). Solutions ă exhibit plasma velocities (M = 1) and temperatures fluxes at the ă plasma-wall boundaries that match with boundary conditions usually ă implemented in fluid codes. Grid convergence and error estimates are ă found to be in agreement with theoretical results obtained for neutral ă fluid conservation equations. The capability of the penalization ă technique is illustrated by introducing the non-collisional plasma ă region expected by the kinetic theory in the immediate vicinity of the ă interface, that is impossible when considering fluid boundary ă conditions. Axisymmetric numerical simulations show the efficiency of ă the method to investigate the large-scale transport at the plasma edge ă including the separatrix and in realistic complex geometries while ă keeping a simple structured grid. (C) 2014 Elsevier Inc. All rights ă reserved.
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak ă with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. <10.1016/j.jcp.2014.05.025>. <hal-01464707>
Romain Nguyen Yen, Dmitry Kolomenskiy, Kai Schneider. Approximation of the Laplace and Stokes operators with Dirichlet ă boundary conditions through volume penalization: a spectral viewpoint. Numerische Mathematik, Springer Verlag, 2014, 128 (2), pp.301-338. Plus de détails...
We report the results of a study on the spectral properties of Laplace ă and Stokes operators modified with a volume penalization term designed ă to approximate Dirichlet conditions in the limit when a penalization ă parameter, , tends to zero. The eigenvalues and eigenfunctions are ă determined either analytically or numerically as functions of , both in ă the continuous case and after applying Fourier or finite difference ă discretization schemes. For fixed , we find that only the part of the ă spectrum corresponding to eigenvalues approaches Dirichlet boundary ă conditions, while the remainder of the spectrum is made of uncontrolled, ă spurious wall modes. The penalization error for the controlled ă eigenfunctions is estimated as a function of and . Surprisingly, in the ă Stokes case, we show that the eigenfunctions approximately satisfy, with ă a precision , Navier slip boundary conditions with slip length equal to ă . Moreover, for a given discretization, we show that there exists a ă value of , corresponding to a balance between penalization and ă discretization errors, below which no further gain in precision is ă achieved. These results shed light on the behavior of volume ă penalization schemes when solving the Navier-Stokes equations, outline ă the limitations of the method, and give indications on how to choose the ă penalization parameter in practical cases.
Romain Nguyen Yen, Dmitry Kolomenskiy, Kai Schneider. Approximation of the Laplace and Stokes operators with Dirichlet ă boundary conditions through volume penalization: a spectral viewpoint. Numerische Mathematik, Springer Verlag, 2014, 128 (2), pp.301-338. <10.1007/s00211-014-0610-8>. <hal-01464705>
Jorge Morales, Matthieu Leroy, Wouter Bos, Kai Schneider. Simulation of confined magnetohydrodynamic flows with Dirichlet boundary conditions using a pseudo-spectral method with volume penalization. Journal of Computational Physics, Elsevier, 2014, 274, pp.64-94. Plus de détails...
A volume penalization approach to simulate magnetohydrodynamic (MHD) flows in confined domains is presented. Here the incompressible visco-resistive MHD equations are solved using parallel pseudo-spectral solvers in Cartesian geometries. The volume penalization technique is an immersed boundary method which is characterized by a high flexibility for the geometry of the considered flow. In the present case, it allows to use other than periodic boundary conditions in a Fourier pseudo-spectral approach. The numerical method is validated and its convergence is assessed for two- and three-dimensional hydrodynamic (HD) and MHD flows, by comparing the numerical results with results from literature and analytical solutions. The test cases considered are two-dimensional Taylor-Couette flow, the $z$-pinch configuration, three dimensional Orszag-Tang flow, ohmic-decay in a periodic cylinder, three-dimensional Taylor-Couette flow with and without axial magnetic field and three-dimensional Hartmann-instabilities in a cylinder with an imposed helical magnetic field.
Jorge Morales, Matthieu Leroy, Wouter Bos, Kai Schneider. Simulation of confined magnetohydrodynamic flows with Dirichlet boundary conditions using a pseudo-spectral method with volume penalization. Journal of Computational Physics, Elsevier, 2014, 274, pp.64-94. <10.1016/j.jcp.2014.05.038>. <hal-00719737>
Denis Martinand, Eric Serre, Richard M. Lueptow. Mechanisms for the transition to waviness for Taylor vortices. Physics of Fluids, American Institute of Physics, 2014, 26 (9), pp.094102. Plus de détails...
Building on the weakly nonlinear amplitude equation of the saturated Taylor vortices developing in a Taylor–Couette cell with a rotating inner cylinder and a fixed outer one, the physical mechanism underlying the destabilization of these vortices resulting in azimuthal waviness is addressed using Floquet analysis. For narrow gap configurations, analysis and direct numerical simulations together with existing experimental results support the idea that the waviness is generated by the axial shear in the azimuthal velocity due to the alternate advection by the Taylor vortices of azimuthal momentum between the cylinders. For wide gap configurations, this mechanism is no longer able to drive the azimuthal waviness and a different mechanism tends to select a subharmonic instability.
Denis Martinand, Eric Serre, Richard M. Lueptow. Mechanisms for the transition to waviness for Taylor vortices. Physics of Fluids, American Institute of Physics, 2014, 26 (9), pp.094102. <10.1063/1.4895400>. <hal-01300402>
Jorge A. Morales, Wouter Bos, Kai Schneider, David Montgomery. The effect of toroidicity on Reversed Field Pinch dynamics. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56, pp.095024 . Plus de détails...
The influence of the curvature of the imposed magnetic field on Reversed Field Pinch dynamics is investigated by comparing the flow of a magnetofluid in a torus with aspect ratio 1.83, with the flow in a periodic cylinder. It is found that an axisymmetric toroidal mode is always present in the toroidal, but absent in the cylindrical configuration. In particular, in contrast to the cylinder, the toroidal case presents a double poloidal recirculation cell with a shear localized at the plasma edge. Quasi-single-helicity states are found to be more persistent in toroidal than in periodic cylinder geometry.
Jorge A. Morales, Wouter Bos, Kai Schneider, David Montgomery. The effect of toroidicity on Reversed Field Pinch dynamics. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56, pp.095024 <10.1088/0741-3335/56/9/095024>. <hal-01026354>
Kai Schneider, Mickaël Paget-Goy, Alberto Verga, Marie Farge. Numerical simulation of flows past flat plates using volume penalization. Computational and Applied Mathematics, Springer Verlag, 2014, 33 (2), pp.481-495. Plus de détails...
We present numerical simulations of two-dimensional viscous incompressible flows past flat plates having different kind of wedges: one tip of the plate is rectangular, while the other tip is either a wedge with an angle of 30∘ or a round shape. We study the shear layer instability of the flow considering different scenarios, either an impulsively started plate or an uniformly accelerated plate, for Reynolds number Re=9500. The volume penalization method, with either a Fourier spectral or a wavelet discretization, is used to model the plate geometry with no-slip boundary conditions, where the geometry of the plate is simply described by a mask function. On both tips, we observe the formation of thin shear layers which are rolling up into spirals and form two primary vortices. The self-similar scaling of the spirals corresponds to the theoretical predictions of Saffman for the inviscid case. At later times, these vortices are advected downstream and the free shear layers undergo a secondary instability. We show that their formation and subsequent dynamics is highly sensitive to the shape of the tips. Finally, we also check the influence of a small riblet, added on the back of the plate on the flow evolution.
Kai Schneider, Mickaël Paget-Goy, Alberto Verga, Marie Farge. Numerical simulation of flows past flat plates using volume penalization. Computational and Applied Mathematics, Springer Verlag, 2014, 33 (2), pp.481-495. <10.1007/s40314-013-0076-9>. <hal-01299239>
A. Salhi, Frank G. Jacobitz, Kai Schneider, Claude Cambon. Nonlinear dynamics and anisotropic structure of rotating sheared turbulence. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89, pp.013020. Plus de détails...
Homogeneous turbulence in rotating shear flows is studied by means of pseudospectral direct numerical simulation and analytical spectral linear theory (SLT). The ratio of the Coriolis parameter to shear rate is varied over a wide range by changing the rotation strength, while a constant moderate shear rate is used to enable significant contributions to the nonlinear interscale energy transfer and to the nonlinear intercomponental redistribution terms. In the destabilized and neutral cases, in the sense of kinetic energy evolution, nonlinearity cannot saturate the growth of the largest scales. It permits the smallest scale to stabilize by a scale-by-scale quasibalance between the nonlinear energy transfer and the dissipation spectrum. In the stabilized cases, the role of rotation is mainly nonlinear, and interacting inertial waves can affect almost all scales as in purely rotating flows. In order to isolate the nonlinear effect of rotation, the two-dimensional manifold with vanishing spanwise wave number is revisited and both two-component spectra and single-point two-dimensional energy components exhibit an important effect of rotation, whereas the SLT as well as the purely two-dimensional nonlinear analysis are unaffected by rotation as stated by the Proudman theorem. The other two-dimensional manifold with vanishing streamwise wave number is analyzed with similar tools because it is essential for any shear flow. Finally, the spectral approach is used to disentangle, in an analytical way, the linear and nonlinear terms in the dynamical equations
A. Salhi, Frank G. Jacobitz, Kai Schneider, Claude Cambon. Nonlinear dynamics and anisotropic structure of rotating sheared turbulence. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89, pp.013020. <10.1103/PhysRevE.89.013020>. <hal-01048730>
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Francois Gallaire, Philippe Meliga, Patrice Laure, Charles N. Baroud. Marangoni induced force on a drop in a Hele Shaw cell. Physics of Fluids, American Institute of Physics, 2014, 26 (6), pp.062105. Plus de détails...
We analyse the force balance on a cylindrical drop in a Hele-Shaw cell, subjected to a Marangoni flow caused by a surface tension gradient. Depth-averaged Stokes equations, called Brinkman equations, are introduced and a general closed form solution is obtained. The validity of the averaging procedure is ascertained by considering a linear surface tension gradient acting on a cylindrical flattened drop. The Marangoni-driven flow field and resulting force predicted by the Brinkman model are seen to match well a full three-dimensional direct numerical simulation. A closed form ex-pression of the force acting on the drop is obtained, calculated from contributions due to the normal viscous stress, tangential viscous stress, and pressure fields, integrated on the drop perimeter. This expression is used to predict the force balance when a stationary droplet is submitted to both a carrier flow and a Marangoni flow. We show that previous results in the literature had underestimated by a factor two the Marangoni-induced force.
Francois Gallaire, Philippe Meliga, Patrice Laure, Charles N. Baroud. Marangoni induced force on a drop in a Hele Shaw cell. Physics of Fluids, American Institute of Physics, 2014, 26 (6), pp.062105. <10.1063/1.4878095>. <hal-01054669>
The paper presents a numerical investigation of the leading-edge vortices generated by rotating triangular wings at Reynolds number Re=250. A series of three-dimensional numerical simulations have been carried out using a Fourier pseudo-spectral method with volume penalization. The transition from stable attachment of the leading-edge vortex to periodic vortex shedding is explored, as a function of the wing aspect ratio and the angle of attack. It is found that, in a stable configuration, the spanwise flow in the recirculation bubble past the wing is due to the centrifugal force, incompressibility and viscous stresses. For the flow outside of the bubble, an inviscid model of spanwise flow is presented.
Jose Joaquin Sanchez-Alvarez, Eric Serre, Emilia Arco, Friedrich.H Busse. Geometry effects on Rayleigh-Benard convection in rotating annular ă layers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89 (6), . Plus de détails...
Rayleigh-Benard convection is investigated in rotating annular cavities ă at a moderate dimensionless rotation rate Omega = 60. The onset of ă convection is in the form of azimuthal traveling waves that set in at ă the sidewalls and at values of the Rayleigh number significantly below ă the value of the onset of convection in an infinitely extended layer. ă The present study addresses the effects of curvature and confinement on ă the onset of sidewall convection by using three-dimensional spectral ă solutions of the Oberbeck-Boussinesq equations. Such solutions ă demonstrate that the curvature of the outer boundary promotes the onset ă of the wall mode, while the opposite curvature of the inner boundary ă tends to delay the onset of the wall mode. An inner sidewall with a ă radius as low as one tenth of its height is sufficient, however, to ă support the onset of a sidewall mode. When radial confinement is ă increased the two independent traveling waves interact and eventually ă merge to form a nearly steady pattern of convection.
Jose Joaquin Sanchez-Alvarez, Eric Serre, Emilia Arco, Friedrich.H Busse. Geometry effects on Rayleigh-Benard convection in rotating annular ă layers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89 (6), <10.1103/PhysRevE.89.063013>. <hal-01464703>
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Stéphane Viazzo, Sébastien Poncet. Numerical simulation of the flow stability in a high aspect ratio Taylor–Couette system submitted to a radial temperature gradient. Computers and Fluids, Elsevier, 2014, 101, pp.15-26. Plus de détails...
From 28 high-order DNS computations, one investigates the formation of instabilities due to the strong competition between an azimuthal flow induced by rotation and an axial flow due to convection in a tall Taylor–Couette apparatus (gamma=80; eta=0.8) submitted to a radial temperature gradient. One explores the richness of the transition diagram that reports seven different flow patterns appearing either as spiral rolls, wavy vortices or a combination of both depending on the Taylor and Rayleigh numbers. The partial spiral regime observed experimentally by Guillerm (2010) is not recovered at very low Rayleigh numbers. The spatio-temporal properties of the different spirals close to the threshold of the primary instability are fairly predicted and a new insight on the flow and thermal structures of the instabilities is gained from this study. Finally, the distributions of the Nusselt number against the Taylor number are established for various Rayleigh numbers.
Stéphane Viazzo, Sébastien Poncet. Numerical simulation of the flow stability in a high aspect ratio Taylor–Couette system submitted to a radial temperature gradient. Computers and Fluids, Elsevier, 2014, 101, pp.15-26. <10.1016/j.compfluid.2014.05.025>. <hal-01083054>
Sébastien Poncet. The stability of a thin water layer over a rotating disk revisited. European Physical Journal Plus, 2014, 129, pp.167. Plus de détails...
The flow driven by a rotating disk of a thin fluid layer in a fixed cylindrical casing is studied by direct numerical simulation and experimental flow visualizations. The characteristics of the flow are first briefly discussed but the focus of this work is to understand the transition to the primary instability. The primary bifurcation is 3D and appears as spectacular sharp-cornered polygonal patterns located along the shroud. The stability diagram is established experimentally in a (Re, G) plane, where G is the aspect ratio of the cavity and Re the rotational Reynolds number and confirmed numerically. The number of vortices scales well with the Ekman number based on the water depth, which confirms the existence of a Stewartsonlayer along the external cylinder. The critical mixed Reynolds number is found to be constant as in other rotating flows involving a shear-layer instability. Hysteresis cycles are observed highlighting the importance of the spin-up and spin-down processes. In some particular cases, a crossflow instability appears under the form of high azimuthal wave number spiral patterns, similar to those observed in a rotor-stator cavity with throughflow and coexists with the polygons. The DNS calculations confirm the experimental results under the flat free surface hypothesis.
Sébastien Poncet. The stability of a thin water layer over a rotating disk revisited. European Physical Journal Plus, 2014, 129, pp.167. <10.1140/epjp/i2014-14167-2>. <hal-01083053>
Marcello Meldi, Hugo Lejemble, Pierre Sagaut. On the emergence of non-classical decay regimes in multiscale/fractal generated isotropic turbulence. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2014, 756, pp.816-843. Plus de détails...
The present paper addresses the issue of finding key parameters that may lead to the occurrence of non-classical decay regimes for fractal/multiscale generated grid turbulence. To this aim, a database of numerical simulations has been generated by the use of the eddy-damped quasi-normal Markovian (EDQNM) model. The turbulence production in the wake of the fractal/multiscale grid is modelled via a turbulence production term based on the forcing term developed for direct numerical simulations (DNS) purposes and the dynamics of self-similar wakes. The sensitivity of the numerical results to the simulation parameters has been investigated successively. The analysis is based on the observation of both the time evolution of the turbulent energy spectrum $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}E(k,t)$ and the decay of the flow statistical quantities, such as the turbulent kinetic energy $\mathcal{K}(t)$ and the energy dissipation rate $\varepsilon (t)$. A satisfactory agreement with existing experimental data published by different research teams is observed. In particular, it is observed that the key parameter that governs the nature of turbulence decay is $\alpha ={d/U_{\infty }}\, {(\varepsilon (0)/\mathcal{K}(0))}={d/L(0)} \, {(\sqrt{\mathcal{K}(0)}/U_{\infty })}$ (with $d$ the bar diameter and $U_{\infty }$ the upstream uniform velocity), which measures the ratio of the time scale largest grid bar $d/U_{\infty }$ to the turbulent time scale $\mathcal{K}(0)/\varepsilon (0)$. Two asymptotic behaviours for $\alpha \rightarrow + \infty $ and $\alpha \rightarrow 0$ are identified: (i) a fast algebraic decay law regime for rapidly decaying production terms, due to strongly modified initial kinetic energy spectrum and (ii) a real exponential decay regime associated with strong, very slowly decaying production terms. The present observations are in full agreement with conclusions drawn from recent fractal grid experiments, and it provides a physical scenario for occurrence of anomalous decay regime which encompasses previous hypotheses.
Marcello Meldi, Hugo Lejemble, Pierre Sagaut. On the emergence of non-classical decay regimes in multiscale/fractal generated isotropic turbulence. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2014, 756, pp.816-843. <10.1017/jfm.2014.476>. <hal-01064518>
Guillaume Fontaine, Sébastien Poncet, Eric Serre. Multidomain Extension of a Pseudospectral Algorithm for the Direct Simulation of Wall-Confined Rotating Flows. M. Azaiez, H. El Fekih, J.S. Hesthaven. Lecture Notes in Computational Science and Engineering, 95, Springer, pp.261 - 271, 2014, . Plus de détails...
In this work, we improve an existing pseudospectral algorithm, in order to extend its properties to a multidomain patching of a rotating cavity. Viscous rotating flows have been widely studied over the last decades, either on industrial or aca-demic approaches. Nevertheless, the range of Reynolds numbers reached in indus-trial devices implies very high resolutions of the spatial problem, which are clearly unreachable using a monodomain approach. Hence, we worked on the multido-main extension of the existing divergence-free Navier-Stokes solver with a Schur approach. The particularity of such an approach is that it does not require any sub-domain superposition: the value of a variable on the boundary between two adjacent subdomains is treated as a boundary condition of a local Helmholtz solver. This value is computed on a direct way via a so-called continuity influence matrix and the derivative jump of an homogeneous solution computed independently on each subdomain. Such a method is known to have both good scalability and accuracy. It has been validated on two well documented three-dimensional rotating flows.
Guillaume Fontaine, Sébastien Poncet, Eric Serre. Multidomain Extension of a Pseudospectral Algorithm for the Direct Simulation of Wall-Confined Rotating Flows. M. Azaiez, H. El Fekih, J.S. Hesthaven. Lecture Notes in Computational Science and Engineering, 95, Springer, pp.261 - 271, 2014, <10.1007/978-3-319-01601-6_21>. <hal-01098589>
Marco Martins Afonso, Simon Mendez, Franck Nicoud. On the damped oscillations of an elastic quasi-circular membrane in a two-dimensional incompressible fluid. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2014, 746, pp.300 -331. Plus de détails...
We propose a procedure--partly analytical and partly numerical--to find the frequency and the damping rate of the small-amplitude oscillations of a massless elastic capsule immersed in a two-dimensional viscous incompressible fluid. The unsteady Stokes equations for the stream function are decomposed onto normal modes for the angular and temporal variables, leading to a fourth-order linear ordinary differential equation in the radial variable. The forcing terms are dictated by the properties of the membrane, and result into jump conditions at the interface between the internal and external media. The equation can be solved numerically, and an excellent agreement is found with a fullycomputational approach we developed in parallel. Comparisons are also shown with the results available in the scientific literature for drops, and a model based on the concept of entrained fluid is presented, which allows for a good representation of the results and a consistent interpretation of the underlying physics.
Marco Martins Afonso, Simon Mendez, Franck Nicoud. On the damped oscillations of an elastic quasi-circular membrane in a two-dimensional incompressible fluid. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2014, 746, pp.300 -331. <10.1017/jfm.2014.135>. <hal-00957710>
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich Busse. Geometry effects on the onset of rotating Rayleigh-Bénard convection in annuli. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89, pp.063013. Plus de détails...
Rayleigh-Bénard convection is investigated in rotating annular cavities at a moderate rotationrate (square root of the Taylor number) Omega= 60. The onset of convection is in the form of azimuthaltraveling waves that set in at the sidewalls and at values of the Rayleigh number significantly belowthe value of the onset of convection in an infinitely extended layer. When curvature effect becomessignificant, the waves traveling along the sidewalls have different critical Rayleigh numbers and com-plex Guinzburg-Landau equations are no longer applicable. The present study addresses the effectsof curvature and confinement on the onset of sidewall convection by using three-dimensional spectralsolutions of the Oberbeck-Boussinesq equations. Such solutions demonstrate that the curvature ofthe outer boundary promotes the onset of the wall mode, while the opposite curvature of the innerboundary tends to delay the onset of the wall mode. When radial confinement is increased the twoindependent traveling waves can interact and eventually merge to form a nearly steady pattern ofconvection.
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich Busse. Geometry effects on the onset of rotating Rayleigh-Bénard convection in annuli. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89, pp.063013. <hal-01087216>
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Clothilde Colin, Patrick Tamain, Philippe Ghendrih, Frederic Schwander, Eric Serre. Impact of a Langmuir probe on turbulence measurements in the Scrape-Off-Layer of tokamaks. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.543-548. Plus de détails...
An issue for Langmuir probe measurements of SOL turbulence concerns the impact of the probe itself on plasma transport. The aim of this paper is to investigate this issue with a synthetic reconstruction of Langmuir probe measurements by inserting a synthetic probe into a 2D fluid SOL turbulence code. The effect of a biased probe is analysed as a function of its size. It is shown that the probe creates a transport barrier whose effect is non-local and affects the current's circulation in the plasma. The plasma density is depleted by the presence of the probe as well as the electrostatic potential. A strong impact on turbulence can also be observed. Such observations imply that the probed turbulence can differ significantly from the probe-free turbulence
Clothilde Colin, Patrick Tamain, Philippe Ghendrih, Frederic Schwander, Eric Serre. Impact of a Langmuir probe on turbulence measurements in the Scrape-Off-Layer of tokamaks. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.543-548. <10.1002/ctpp.201410087>. <hal-01019696>
Philippe Meliga, Edouard Boujo, Gregory Pujals, François Gallaire. Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder. Physics of Fluids, American Institute of Physics, 2014, 26, pp.26,104101. Plus de détails...
We use adjoint-based gradients to analyze the sensitivity of the drag force on a square cylinder. At Re = 40, the flow settles down to a steady state. The quantity of interest in the adjoint formulation is the steady asymptotic value of drag reached after the initial transient, whose sensitivity is computed solving a steady adjoint problem from knowledge of the stable base solution. At Re = 100, the flow develops to the time-periodic, vortex-shedding state. The quantity of interest is rather the time-averaged mean drag, whose sensitivity is computed integrating backwards in time an unsteady adjoint problem from knowledge of the entire history of the vortex-shedding solution. Such theoretical frameworks allow us to identify the sensitive regions without com-puting the actually controlled states, and provide a relevant and systematic guideline on where in the flow to insert a secondary control cylinder in the attempt to reduce drag, as established from comparisons with dedicated numerical simulations of the two-cylinder system. For the unsteady case at Re = 100, we also compute an approxi-mation to the mean drag sensitivity solving a steady adjoint problem from knowledge of only the mean flow solution, and show the approach to carry valuable information in view of guiding relevant control strategy, besides reducing tremendously the re-lated numerical effort. An extension of this simplified framework to turbulent flow regime is examined revisiting the widely benchmarked flow at Reynolds number Re = 22 000, the theoretical predictions obtained in the frame of unsteady Reynolds-averaged Navier–Stokes modeling being consistent with experimental data from the literature. Application of the various sensitivity frameworks to alternative control objectives such as increasing the lift and reducing the fluctuating drag and lift is also discussed and illustrated with a few selected examples.
Philippe Meliga, Edouard Boujo, Gregory Pujals, François Gallaire. Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder. Physics of Fluids, American Institute of Physics, 2014, 26, pp.26,104101. <10.1063/1.4896941>. <hal-01082600v2>
Alex Skillen, Alistair Revell, Alfredo Pinelli, Ugo Piomelli, Julien Favier. Flow over a Wing with Leading-Edge Undulations. AIAA Journal, American Institute of Aeronautics and Astronautics, 2014, 53 (2), pp.464-472. Plus de détails...
The stall-delaying properties of the humpback whale flipper have been observed and quantified in recent years, through both experimental and numerical studies. In the present work we report numerical simulations of an infinite span wing with an idealised representation of this geometry, at a Reynolds number of 1.2 × 105 . Us- ing Large Eddy Simulation, we first establish an adequate spatial resolution before also examining the spanwise extent of the domain. We then proceed to analyse these results to provide an explanation of the conditions that drive the lift observed be- yond the conventional stall angle. The undulating leading-edge geometry gives rise to a span-wise pressure gradient that drives a secondary flow towards the regions of minimum chord. In turn, this leads to the entrainment of higher-momentum fluid into the region behind the maximum chord, which energises the boundary layer and delays stall. Aside from demonstrating a significant post-stall lift, the undulations also have the added benefit of substantially reducing lift fluctuations.
Alex Skillen, Alistair Revell, Alfredo Pinelli, Ugo Piomelli, Julien Favier. Flow over a Wing with Leading-Edge Undulations. AIAA Journal, American Institute of Aeronautics and Astronautics, 2014, 53 (2), pp.464-472. <10.2514/1.J053142>. <hal-01069899>
Alejandro Paredes, Eric Serre, Frédéric Schwander, Philippe Ghendrih, Patrick Tamain. Numerical fluid modelling of the plasma edge response to a 3D object and application to mach probe measurements. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.373-377. Plus de détails...
The penalization method is used to model the interaction of 3D probe with an isothermal plasma. Density maps show that the region perturbed by the obstacle, is not restricted to its near neighbourhood, but can extend to the whole SOL. In the particular case of a probe, which is used to measure local plasma parameters, this impact can lead to violation of assumptions of locality of the perturbation usually used in determining Mach number from the imbalance in density on both sides of the probe.
Alejandro Paredes, Eric Serre, Frédéric Schwander, Philippe Ghendrih, Patrick Tamain. Numerical fluid modelling of the plasma edge response to a 3D object and application to mach probe measurements. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.373-377. <10.1002/ctpp.201410028>. <hal-01050666>
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (122001), . Plus de détails...
We present a comprehensive picture of the mechanisms driving the transition from subsonic to supersonic flows in tokamak plasmas. We demonstrate that supersonic parallel flows into the divertor volume are ubiquitous at low density and governed by the divertor magnetic geometry. As the density is increased, subsonic divertor plasmas are recovered. On detachment, we show the change in particle source can also drive the transition to a supersonic regime. The comprehensive theoretical analysis is completed by simulations in ITER geometry. Such results are essential in assessing the divertor performance and when interpreting measurements and experimental evidence. The generation of large-scale flows in laboratory plasma is a highly non-linear problem. In a standard fashion it is considered that the flows remain subsonic away from the wall, the occurrence of supersonic flows being singular. We show here that the geometrical features of key configurations for fusion plasma can lead to supersonic flows.
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (122001), <10.1088/0741-3335/56/12/122001>. <hal-01225185>
Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, Marie Farge. Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89 (3), pp.033013. Plus de détails...
Small-scale anisotropic intermittency is examined in three-dimensional incompressible magnetohydrodynamic turbulence subjected to a uniformly imposed magnetic field. Orthonormal wavelet analyses are applied to direct numerical simulation data at moderate Reynolds number and for different interaction parameters. The magnetic Reynolds number is sufficiently low such that the quasistatic approximation can be applied. Scale-dependent statistical measures are introduced to quantify anisotropy in terms of the flow components, either parallel or perpendicular to the imposed magnetic field, and in terms of the different directions. Moreover, the flow intermittency is shown to increase with increasing values of the interaction parameter, which is reflected in strongly growing flatness values when the scale decreases. The scale-dependent anisotropy of energy is found to be independent of scale for all considered values of the interaction parameter. The strength of the imposed magnetic field does amplify the anisotropy of the flow.
Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, Marie Farge. Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89 (3), pp.033013. <10.1103/physreve.89.033013>. <hal-01087726>
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.555-559. Plus de détails...
The 3D fluid turbulence code TOKAM3X is used to investigate the 3D properties of edge turbulent transport and their impact on poloidal asymmetries. Simulations are run in circular limited plasmas in a domain covering both closed and open flux surfaces. Turbulence characteristics exhibit large inhomogeneities both in the radial and poloidal directions reminiscent of experimental observations. The low field side mid-plane in particular is found to be locally more fluctuating and intermittent than the rest of the Scrape-Off-Layer (SOL). As a consequence of this asymmetry, radial turbulent transport, that represents 80 to 90% of the total radial flux, is strongly ballooned, with 75% of the flux flowing through LFS. The equilibrium of the edge plasma is impacted by this asymmetry through the existence of large amplitude asymmetric parallel flows as well as through the development of poloidally asymmetric radial decay lengths making it impossible to define a single SOL width.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.555-559. <10.1002/ctpp.201410017>. <hal-01053290>
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. Plus de détails...
To properly address turbulent transport in the edge plasma region of a tokamak, it is mandatory to describe the particle and heat outflow on wall components, using an accurate representation of the wall geometry. This is challenging for many plasma transport codes, which use a structured mesh with one coordinate aligned with magnetic surfaces. We propose here a penalization technique that allows modelingof particle and heat transport using such structured mesh, while also accounting for geometrically complex plasma-facing components. Solid obstacles are considered as particle and momentum sinks whereas ionic and electronic temperature gradients are imposed on both sides of the obstacles along the magnetic field direction using delta functions (Dirac). Solutions exhibit plasma velocities (M=1) and temperatures fluxes at the plasma–wall boundaries that match with boundary conditions usually implemented in fluid codes. Grid convergence and error estimates are found to be in agreement with theoretical results obtained for neutral fluid conservation equations. The capability of the penalization technique is illustrated by introducing the non-collisional plasma region expected by the kinetic theory in the immediate vicinity of the interface, that is impossible when considering fluid boundary conditions. Axisymmetric numerical simulations show the efficiency of the method to investigate the large-scale transport at the plasma edge including the separatrix and in realistic complex geometries while keeping a simple structured grid.
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. <hal-01087225>
Nils Tilton, Eric Serre, Denis Martinand, Richard M. Lueptow. A 3D pseudospectral algorithm for fluid flows with permeable walls. Application to filtration. Computers and Fluids, Elsevier, 2014, 93, pp.129-145. Plus de détails...
The present work proposes a Chebyshev-collocation Fourier-Galerkin pseudospectral method for simulating unsteady, three-dimensional, fluid flows in cylindrical geometries with pressure-driven flow through permeable boundaries. Such systems occur in diverse applications and are challenging to simulate due to an additional velocity-pressure coupling on the permeable walls through Darcy's law. The present work extends the projection method of Raspo et al. (2002) to assure Darcy's law is satisfied exactly. A multidomain solver allows the efficient treatment of open boundary conditions that necessitate permeability buffers and a sponge layer. The method is spectrally convergent, and we demonstrate that pressure-prediction is necessary to obtain second-order temporal accuracy. The ability of the method to simulate complicated physical systems is demonstrated by simulating subcritical and supercritical flows in rotating filtration in Taylor-Couette cells. For subcritical cases, numerical results show excellent agreement with analytical solutions. For supercritical cases, the numerical method accurately resolves convectively and absolutely unstable flows with traveling toroidal and helical vortical structures that are in good agreement with a local linear stability analysis and experimental observations.
Nils Tilton, Eric Serre, Denis Martinand, Richard M. Lueptow. A 3D pseudospectral algorithm for fluid flows with permeable walls. Application to filtration. Computers and Fluids, Elsevier, 2014, 93, pp.129-145. <10.1016/j.compfluid.2014.01.003>. <hal-01053339>
Julien Favier, Alistair Revell, Alfredo Pinelli. A Lattice Boltzmann - Immersed Boundary method to simulate the fluid interaction with moving and slender flexible objects. Journal of Computational Physics, Elsevier, 2014, 261, pp.145-161. Plus de détails...
A numerical approach based on the Lattice Boltzmann and Immersed Boundary methods is pro- posed to tackle the problem of the interaction of moving and/or deformable slender solids with an incompressible fluid flow. The method makes use of a Cartesian uniform lattice that encom- passes both the fluid and the solid domains. The deforming/moving elements are tracked through a series of Lagrangian markers that are embedded in the computational domain. Differently from classical projection methods applied to advance in time the incompressible Navier-Stokes equa- tions, the baseline Lattice Boltzmann fluid solver is free from pressure corrector step, which is known to affect the accuracy of the boundary conditions. Also, in contrast to other immersed boundary methods proposed in the literature, the proposed algorithm does not require the in- troduction of any empirical parameter. In the case of rigid bodies, the position of the markers delimiting the surface of an object is updated by tracking both the position of the center of mass of the object and its rotation using Newton's Laws and the conservation of angular momentum. The dynamics of a flexible slender structure is determined as a function of the forces exerted by the fluid, its flexural rigidity and the tension necessary to enforce the filament inextensibility. For both rigid and deformable bodies, the instantaneous no-slip and impermeability conditions on the solid boundary are imposed via external and localized body forces which are consistently introduced into the Lattice Boltzmann equation. The validation test-cases for rigid bodies in- clude the case of an impulsively started plate and the sedimentation of particles under gravity in a fluid initially at rest. For the case of deformable slender structures we consider the beating of both a single filament and a pair filaments induced by the interaction with an incoming uniformly streaming flow.
Julien Favier, Alistair Revell, Alfredo Pinelli. A Lattice Boltzmann - Immersed Boundary method to simulate the fluid interaction with moving and slender flexible objects. Journal of Computational Physics, Elsevier, 2014, 261, pp.145-161. <10.1016/j.jcp.2013.12.052>. <hal-00822044>
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.432-436. Plus de détails...
We present numerical simulations of plasma transport obtained with the SOLEDGE2D code coupled to the EIRENE Montecarlo code for neutrals. We consider a double null magnetic configuration in a WEST geometry. Density and temperatures parallel profiles in the SOL domain are presented as well as Mach profile. We detail how using the penalization technique we are able to model plasma transport up to the first wall having access to energy and particle fluxes on the entire chamber wall. Moreover, we present the computed 2D contour map of the plasma mach number and of the magnitude of the ionisation source term in the whole poloidal section, emphasizing how complex and realistic geometries can be handled thanks to the penalization technique.
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.432-436. <10.1002/ctpp.201410018>. <hal-01050505>
Roux B., Bohbot J., Tran Q. H., Sagaut P.. Prediction of cyclic combustion variability in internal combustion engines via coupled 1D-3D LES methods. E. Oate, J. Oliver and A. Huerta. Proceedings of the 6th European Conference on Computational Fluid Dynamics, pp.5474--5485, 2014. Plus de détails...
Roux B., Bohbot J., Tran Q. H., Sagaut P.. Prediction of cyclic combustion variability in internal combustion engines via coupled 1D-3D LES methods. E. Oate, J. Oliver and A. Huerta. Proceedings of the 6th European Conference on Computational Fluid Dynamics, pp.5474--5485, 2014. <hal-01307241>
Bikash Sahoo, Saied Abbasbandy, Sébastien Poncet. A brief note on the computation of the Bödewadt flow with Navier slip boundary conditions. Computers and Fluids, Elsevier, 2014, 90, pp.133-137. Plus de détails...
In this short communication, numerical solutions are obtained for the steady Bödewadt flow of a viscous fluid subject to partial slip boundary conditions. The resulting system of nonlinear and fully coupled similarity equations are integrated accurately by a finite difference scheme and by the Keller-box method. It is observed that slip has a prominent effect on the velocity field, reducing drastically the axial velocity and the pressure. Moreover, the torque required to maintain the disk at rest decreases for increasing values of slip.
Bikash Sahoo, Saied Abbasbandy, Sébastien Poncet. A brief note on the computation of the Bödewadt flow with Navier slip boundary conditions. Computers and Fluids, Elsevier, 2014, 90, pp.133-137. <10.1016/j.compfluid.2013.11.020>. <hal-00976676>
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.378-382. Plus de détails...
To support ITER divertor design, the WEST project on Tore Supra aims at studying high heat fluxes on tungsten monoblock during long pulses. In that persective, a particular attention is paid to simulate the edge plasma interaction with complex PFCs using the transport code SOLEDGE2D-EIRENE. The plasma response to a heating and puffing scenario is described as well as the so-called divertor density regimes, characterizing the operational domain of the WEST divertor. These results are compared for two different magnetic configurations: a semi-open double null divertor with the X-point away from the target plates and a shallow divertor configuration with the X-point close to the targets.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.378-382. <10.1002/ctpp.201410026>. <hal-01053281>
Marie Farge, H. Keith Moffatt, Kai Schneider. FOREWORD: Turbulence Colloquium Marseille 2011. Journal of Turbulence, Taylor & Francis, 2013, 14 (9), pp.39-42. Plus de détails...
Marie Farge, H. Keith Moffatt, Kai Schneider. FOREWORD: Turbulence Colloquium Marseille 2011. Journal of Turbulence, Taylor & Francis, 2013, 14 (9), pp.39-42. <10.1080/14685248.2013.851836>. <hal-01300038>