Publications de l'équipe Instabilités, Turbulence & Contrôle
2018
Yongliang Feng, Muhammad Tayyab, Pierre Boivin. A Lattice-Boltzmann model for low-Mach reactive flows. Combustion and Flame, Elsevier, 2018, 196, pp.249 - 254. 〈10.1016/j.combustflame.2018.06.027〉. 〈hal-01832640〉 Plus de détails...
A new Lattice-Boltzmann model for low-Mach reactive flows is presented. Based on standard lattices, the model is easy to implement, and is the first, to the authors' knowledge, to pass the classical freely propagating flame test case as well as the counterflow diffusion flame, with strains up to extinction. For this presentation, simplified transport properties are considered, each species being assigned a separate Lewis number. In addition, the gas mixture is assumed to be calorically perfect. Comparisons with reference solutions show excellent agreement for mass fraction profiles, flame speed in premixed mixtures, as well as maximum temperature dependence with strain rate in counterflow diffusion flames.
Yongliang Feng, Muhammad Tayyab, Pierre Boivin. A Lattice-Boltzmann model for low-Mach reactive flows. Combustion and Flame, Elsevier, 2018, 196, pp.249 - 254. 〈10.1016/j.combustflame.2018.06.027〉. 〈hal-01832640〉
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Determination of Diffusion Coefficient in Droplet Evaporation Experiment Using Response Surface Method. Microgravity Science and Technology, Springer, 2018, 30, 〈10.1007/s12217-018-9645-2〉. 〈hal-01847206〉 Plus de détails...
Evaporation of a liquid droplet resting on a heated substrate is a complex free-surface advection-diffusion problem, in which the main driving force of the evaporation is the vapor concentration gradient across the droplet surface. Given the uncertainty associated with the diffusion coefficient of the vapor in the atmosphere during space evaporation experiments due to the environmental conditions, a simple and accurate determination of its value is of paramount importance for a better understanding of the evaporation process. Here we present a novel approach combining numerical simulations and experimental results to address this issue. Specifically, we construct a continuous function of output using a Kriging-based response surface method, which allows to use the numerical results as a black-box with a limited number of inputs and outputs. Relevant values of the diffusion coefficient can then be determined by solving an inverse problem which is based on accessible experimental data and the proposed response surface. In addition, on the basis of our numerical simulation results, we revisit a widely used formula for the prediction of the evaporation rate in the literature and propose a refined expression for the droplets evaporating on a heated substrate.
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Determination of Diffusion Coefficient in Droplet Evaporation Experiment Using Response Surface Method. Microgravity Science and Technology, Springer, 2018, 30, 〈10.1007/s12217-018-9645-2〉. 〈hal-01847206〉
Jérôme Jacob, Pierre Sagaut. Wind comfort assessment by means of large eddy simulation with lattice Boltzmann method in full scale city area. Building and Environment, Elsevier, 2018, 139, pp.110 - 124. 〈10.1016/j.buildenv.2018.05.015〉. 〈hal-01819248〉 Plus de détails...
Jérôme Jacob, Pierre Sagaut. Wind comfort assessment by means of large eddy simulation with lattice Boltzmann method in full scale city area. Building and Environment, Elsevier, 2018, 139, pp.110 - 124. 〈10.1016/j.buildenv.2018.05.015〉. 〈hal-01819248〉
E. Alekseenko, B. Roux. Wind effect on bottom shear stress, erosion and redeposition on Zostera noltei restoration in a coastal lagoon; part 2. Estuarine, Coastal and Shelf Science, Elsevier, In press, 〈10.1016/j.ecss.2018.05.022〉. 〈hal-01813834〉 Plus de détails...
E. Alekseenko, B. Roux. Wind effect on bottom shear stress, erosion and redeposition on Zostera noltei restoration in a coastal lagoon; part 2. Estuarine, Coastal and Shelf Science, Elsevier, In press, 〈10.1016/j.ecss.2018.05.022〉. 〈hal-01813834〉
E. Alekseenko, Bernard Roux. Contribution to remediation of brackish lagoon: 3D simulation of salinity, bottom currents and resuspension of bottom sediments by strong winds. Estuarine, Coastal and Shelf Science, Elsevier, In press, 〈10.1016/j.ecss.2018.05.021〉. 〈hal-01813824〉 Plus de détails...
This work concerns the modelling and numerical simulation of the 3D salinity and current distribution in a very shallow Mediterranean lagoon subject to strong winds which create intensive resuspension of polluted bottom sediments. We consider wind speeds of 10 m/s and 20 m/s in the two dominant wind directions (N-NW and S-SE). This study is made for different scenarios of flow exchanges with the surrounding hydrosystems: a brackish lagoon on the North (the Etang de Berre), the Cadiere River on the East, and a brackish channel on the South (the Rove channel). The bottom shear stress (BSS) are compared to the BBS threshold given in the literature in terms of the bottom roughness. It permits to determine which kind of bottom sediments (muds and sands) will be resuspended by each wind. The bottom currents permit to predict in which direction the suspended sediments will be moved and where are the sedimentary deposit zones. It provides a guide for the specialists of remediation of the lagoon for a mechanical extraction of sediments in such zones. In addition, numerical experiments have been performed to understand how the salinity distribution depends on the flow exchanges with the two brackish surrounding hydrosystems. This new knowledge will permit the owner of this lagoon to know how to maintain efficiently the level of salinity in the suitable range.
E. Alekseenko, Bernard Roux. Contribution to remediation of brackish lagoon: 3D simulation of salinity, bottom currents and resuspension of bottom sediments by strong winds. Estuarine, Coastal and Shelf Science, Elsevier, In press, 〈10.1016/j.ecss.2018.05.021〉. 〈hal-01813824〉
Jessica Sari, Francesco Cremonesi, Mehdi Khalloufi, François Cauneau, Philippe Meliga, et al.. Anisotropic adaptive stabilized finite element solver for RANS models. International Journal for Numerical Methods in Fluids, Wiley, 2018, 86 (11), pp.717-736. 〈10.1002/fld.4475〉. 〈hal-01629274〉 Plus de détails...
Aerodynamic characteristics of various geometries are predicted using a finite element formulation coupled with several numerical techniques to ensure stability and accuracy of the method. First, an edge based error estimator and anisotropic mesh adaptation are used to detect automatically all flow features under the constraint of a fixed number of elements, thus controlling the computational cost. A Variational MultiScale stabilized finite element method is employed to solve the incompressible Navier-Stokes equations. Finally, the Spalart-Allmaras turbulence model is solved using the Streamline Upwind Petrov-Galerkin (SUPG) method. This paper is meant to show that the combination of anisotropic unsteady mesh adaptation with stabilized finite element methods provides an adequate framework for solving turbulent flows at high Reynolds numbers. The proposed method was validated on several test cases by confrontation with literature of both numerical and experimental results, in terms of accuracy on the prediction of the drag and lift coefficients as well as their evolution in time for unsteady cases. This article is protected by copyright. All rights reserved.
Jessica Sari, Francesco Cremonesi, Mehdi Khalloufi, François Cauneau, Philippe Meliga, et al.. Anisotropic adaptive stabilized finite element solver for RANS models. International Journal for Numerical Methods in Fluids, Wiley, 2018, 86 (11), pp.717-736. 〈10.1002/fld.4475〉. 〈hal-01629274〉
Journal: International Journal for Numerical Methods in Fluids
Pierre-Yves Passaggia, Uwe Ehrenstein. Optimal control of a separated boundary-layer flow over a bump. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 840, pp.238 - 265. 〈10.1017/jfm.2018.6〉. 〈hal-01708850〉 Plus de détails...
Pierre-Yves Passaggia, Uwe Ehrenstein. Optimal control of a separated boundary-layer flow over a bump. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 840, pp.238 - 265. 〈10.1017/jfm.2018.6〉. 〈hal-01708850〉
Myriam Slama, Cédric Leblond, Pierre Sagaut. A Kriging-based elliptic extended anisotropic model for the turbulent boundary layer wall pressure spectrum. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 840, pp.25 - 55. 〈10.1017/jfm.2017.810〉. 〈hal-01706751〉 Plus de détails...
The present study addresses the computation of the wall pressure spectrum for a turbulent boundary layer flow without pressure gradient, at high Reynolds numbers, using a new model, the Kriging-based elliptic extended anisotropic model (KEEAM). A space–time solution to the Poisson equation for the wall pressure fluctuations is used. Both the turbulence–turbulence and turbulence–mean shear interactions are taken into account. It involves the mean velocity field and space–time velocity correlations which are modelled using Reynolds stresses and velocity correlation coefficients. We propose a new model, referred to as the extended anisotropic model, to evaluate the latter in all regions of the boundary layer. This model is an extension of the simplified anisotropic model of Gavin (PhD thesis, 2002, The Pennsylvania State University, University Park, PA) which was developed for the outer part of the boundary layer. It relies on a new expression for the spatial velocity correlation function and new parameters calibrated using the direct numerical simulation results of Sillero et al. (Phys. Fluids, vol. 26, 2014, 105109). Spatial correlation coefficients are related to space–time coefficients with the elliptic model of He & Zhang (Phys. Rev. E, vol. 73, 2006, 055303). The turbulent quantities necessary for the pressure computation are obtained by Reynolds-averaged Navier–Stokes solutions with a Reynolds stress turbulence model. Then, the pressure correlations are evaluated with a self-adaptive sampling strategy based on Kriging in order to reduce the computation time. The frequency and wavenumber–frequency wall pressure spectra obtained with the KEEAM agree well with empirical models developed for turbulent boundary layer flows without pressure gradient.
Myriam Slama, Cédric Leblond, Pierre Sagaut. A Kriging-based elliptic extended anisotropic model for the turbulent boundary layer wall pressure spectrum. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 840, pp.25 - 55. 〈10.1017/jfm.2017.810〉. 〈hal-01706751〉
E. Alekseenko, Bernard Roux. Numerical simulation of the wind influence on bottom shear stress and salinity fields in areas of Zostera noltei replanting in a Mediterranean coastal lagoon . Progress in Oceanography, Elsevier, 2018, 163, pp.147-160. 〈hal-01813850〉 Plus de détails...
The paper concerns the numerical simulation of the wind influence on bottom shear stress and salinity fields in a semi-enclosed coastal lagoon (Etang de Berre) which is connected to the Mediterranean through a long and narrow channel (called Caronte). Two different scenarios are considered. The first scenario (scen.#1), starting with an homogeneous salinity of S=20 PSU and without wind forcing, studies a stratification process under the influence of a periodic seawater inflow and a strong freshwater inflow from an hydropower plant (250 m3/s). Then, in the second scenario (scen.#2), we study how a strong wind of 80 km/h can destroy the haline stratification obtained at the end of scen.#1. The MARS3D numerical model is used to analyze the 3D current and salinity distribution induced by these three meteorological, oceanic and anthropogenic forcings in this lagoon and in the Caronte channel.The main goal is to determine the bottom shear stress (BSS) in the nearshore areas of Zostera noltei replanting, and to compare it with the threshold for erosion of the bottom sediments for different bottom roughness parameters.The most interesting results concern the four nearshore replanting areas; two are situated on the eastern side of EB and two on the western side. The results of scen.#2 show that all these areas are subject to a downwind coastal jet. The destratification process is very beneficial; salinity always remains greater than 12 PSU for a N-NW wind of 80 km
E. Alekseenko, Bernard Roux. Numerical simulation of the wind influence on bottom shear stress and salinity fields in areas of Zostera noltei replanting in a Mediterranean coastal lagoon . Progress in Oceanography, Elsevier, 2018, 163, pp.147-160. 〈hal-01813850〉
Marcello Meldi, Pierre Sagaut. Investigation of anomalous very fast decay regimes in homogeneous isotropic turbulence. Journal of Turbulence, Taylor & Francis, 2018, 19 (5), pp.390 - 413. 〈10.1080/14685248.2018.1450506〉. 〈hal-01816010〉 Plus de détails...
The emergence of anomalous fast decay regimes in homogeneous isotropic turbulence (HIT) decay is investigated via both theoretical analysis and eddy-damped quasi-normal Markovian simulations. The work provides new insight about a fundamental issue playing a role in HIT decay, namely the influence of non-standard shapes of the energy spectrum, in particular in the large energetic scale region. A detailed analysis of the kinetic energy spectrum E(k) and the non-linear energy transfer T(k) shows that anomalous decay regimes are associated with the relaxation of initial energy spectra which exhibit a bump at energetic scales. This feature induces an increase in the energy cascade rate, toward solutions with a smooth shape at the spectrum peak. Present results match observations reported in wind-tunnel experiments dealing with turbulence decay in the wake of grids and bluff bodies, including scaling laws for the dissipation parameter C-E. They also indicate that the ratio between the initial eddy turnover time and the advection time determines of how fast anomalous regimes relax toward classical turbulence free-decay. This parameter should be used for consistent data comparison and it opens perspectives for the control of multiscale effects in industrial applications.
Marcello Meldi, Pierre Sagaut. Investigation of anomalous very fast decay regimes in homogeneous isotropic turbulence. Journal of Turbulence, Taylor & Francis, 2018, 19 (5), pp.390 - 413. 〈10.1080/14685248.2018.1450506〉. 〈hal-01816010〉
Philippe Meliga, E. Boujo, M. Meldi, F. Gallaire. Revisiting the drag reduction problem using adjoint-based distributed forcing of laminar and turbulent flows over a circular cylinder. European Journal of Mechanics - B/Fluids, Elsevier, 2018, 〈10.1016/j.euromechflu.2018.03.009〉. 〈hal-01789049〉 Plus de détails...
Philippe Meliga, E. Boujo, M. Meldi, F. Gallaire. Revisiting the drag reduction problem using adjoint-based distributed forcing of laminar and turbulent flows over a circular cylinder. European Journal of Mechanics - B/Fluids, Elsevier, 2018, 〈10.1016/j.euromechflu.2018.03.009〉. 〈hal-01789049〉
Olivier Lafforgue, Isabelle Seyssiecq, Sébastien Poncet, Julien Favier. Rheological properties of synthetic mucus for airway clearance. Journal of Biomedical Materials Research Part A, Wiley, 2018, 106 (2), pp.386 - 396. 〈10.1002/jbm.a.36251〉. 〈hal-01678912〉 Plus de détails...
In this work, a complete rheological characterization of bronchial mucus simulants based on the composition proposed by Zahm et al. [1] is presented. Dynamic Small Amplitude Oscillatory Shear (SAOS) experiments, Steady State (SS) flow measurements and three Intervals Thixotropy Tests (3ITT), are carried out to investigate the global rheological complexities of simulants (viscoelasticity, viscoplasticity, shear-thinning and thixotropy) as a function of scleroglucan concentrations (0.5 to 2wt%) and under temperatures of 20 and 37 °C. SAOS measurements show that the limit of the linear viscoelastic range as well as the elasticity both increase with increasing sclerogucan concentrations. Depending on the sollicitation frequency, the 0.5wt% gel response is either liquid-like or solid-like, whereas more concentrated gels show a solid-like response over the whole frequency range. The temperature dependence of gels response is negligible in the 20-37°C range. The Herschel-Bulkley (HB) model is chosen to fit the SS flow curve of simulants. The evolution of HB parameters versus polymer concentration show that both shear-thinning and viscoplasticity increase with increasing concentrations. 3ITTs allow calculation of recovery thixotropic times after shearings at 100s-1 or 1.6s-1. Empiric correlations are proposed to quantify the effect of polymer concentration on rheological parameters of mucus simulants.
Olivier Lafforgue, Isabelle Seyssiecq, Sébastien Poncet, Julien Favier. Rheological properties of synthetic mucus for airway clearance. Journal of Biomedical Materials Research Part A, Wiley, 2018, 106 (2), pp.386 - 396. 〈10.1002/jbm.a.36251〉. 〈hal-01678912〉
Journal: Journal of Biomedical Materials Research Part A
Pierre Magnico. Spatial distribution of mechanical forces and ionic flux in electro-kinetic instability near a permselective membrane. Physics of Fluids, American Institute of Physics, 2018, 30 (1), pp.014101. 〈10.1063/1.5007930〉. 〈hal-01682986〉 Plus de détails...
This paper is devoted to the numerical investigation of electro-kinetic instability in a polarization layer next to a cation-exchange membrane. An analysis of some properties of the electro-kinetic instability is followed by a detailed description of the fluid flow structure and of the spatial distribution of the ionic flux. In this aim, the Stokes-Poisson-Nernst-Planck equation set is solved until the Debye length scale. The results show that the potential threshold of the marginal instability and the current density depend on the logarithm of the concentration at the membrane surface. The size of the stable vortices seems to be an increasing function of the potential drop. The fluid motion is induced by the electric force along the maximum concentration in the extended space charge (ESC) region and by the pressure force in the region around the inner edge of the ESC layer. Two spots of kinetic energy are located in the ESC region and between the vortices. The cationic motion, controlled by the electric field and the convection, presents counter-rotating vortices in the stagnation zone located in the fluid ejection region. The anion transport is also characterized by two independent layers which contain counter-rotating vortices. The first one is in contact with the stationary reservoir. In the second layer against the membrane, the convection, and the electric field control, the transversal motion, the Fickian diffusion, and the convection are dominant in the longitudinal direction. Finally, the longitudinal disequilibrium of potential and pressure along the membrane is analyzed.
Pierre Magnico. Spatial distribution of mechanical forces and ionic flux in electro-kinetic instability near a permselective membrane. Physics of Fluids, American Institute of Physics, 2018, 30 (1), pp.014101. 〈10.1063/1.5007930〉. 〈hal-01682986〉
G Gallo, N. Fedorczak, S Elmore, M Maurizio, H Reimerdes, et al.. Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (1), pp.014007. 〈10.1088/1361-6587/aa857b〉. 〈hal-01713287〉 Plus de détails...
A deep understanding of plasma transport at the edge of magnetically confined fusion plasmas is needed for the handling and control of heat loads on the machine first wall. Experimental observations collected on a number of tokamaks over the last three decades taught us that heat flux profiles at the divertor targets of X-point configurations can be parametrized by using two scale lengths for the scrape-off layer (SOL) transport, separately characterizing the main SOL (lambda(q)) and the divertor SOL (S-q). In this work we challenge the current interpretation of these two scale lengths as well as their dependence on plasma parameters by studying the effect of divertor geometry modifications on heat exhaust in the Tokamak a Configuration Variable. In particular, a significant broadening of the heat flux profiles at the outer divertor target is diagnosed while increasing the length of the outer divertor leg in lower single null, Ohmic, L-mode discharges. Efforts to reproduce this experimental finding with both diffusive (SolEdge2D-EIRENE) and turbulent (TOKAM3X) modelling tools confirm the validity of a diffusive approach for simulating heat flux profiles in more traditional, short leg, configurations while highlighting the need of a turbulent description for modified, long leg, ones in which strongly asymmetric divertor perpendicular transport develops.
G Gallo, N. Fedorczak, S Elmore, M Maurizio, H Reimerdes, et al.. Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (1), pp.014007. 〈10.1088/1361-6587/aa857b〉. 〈hal-01713287〉
Xun Wang, Shahram Khazaie, Dimitri Komatitsch, Pierre Sagaut. Sound-Source Localization in Range-Dependent Shallow-Water Environments Using a Four-Layer Model. IEEE Journal of Oceanic Engineering, Institute of Electrical and Electronics Engineers, 2017, pp.1 - 9. 〈10.1109/JOE.2017.2775978〉. 〈hal-01702364〉 Plus de détails...
Sound-source localization in shallow water is a difficult task due to the complicated environment, e.g., complex sound-speed profile and irregular water bottom reflections. Full-wave numerical techniques are currently able to accurately simulate the propagation of sound waves in such complex environments. However, the source localization problem, which generally involves a large number of sound propagation calculations, still requires a fast computation of the wave equation, and thus a simplified model is well advised. In this paper, a four-layer model is considered, which is able to approximate a wide range of shallow-water environments, particularly those in summer conditions. More specifically, the medium is assumed to be horizontally stratified and vertically divided into four layers, and the sound speed in each layer is assumed to be constant or varying linearly. Under this assumption, the wave propagation can be rapidly computed via a classical wave number integration method. The main contribution of this paper is to show the suitability of the four-layer model in terms of source localization in a complex (range-dependent) environment. The sound-speed profile is assumed to be vertically irregular and horizontally slowly varying and the bottom is nonflat. In the forward problem, sound propagation in complex underwater environments is simulated via a time-domain full-wave simulation approach called the spectral-element method. The source localization error due to model imprecision is analyzed.
Xun Wang, Shahram Khazaie, Dimitri Komatitsch, Pierre Sagaut. Sound-Source Localization in Range-Dependent Shallow-Water Environments Using a Four-Layer Model. IEEE Journal of Oceanic Engineering, Institute of Electrical and Electronics Engineers, 2017, pp.1 - 9. 〈10.1109/JOE.2017.2775978〉. 〈hal-01702364〉
Here, we explain the phenomenon of focusing using the numerical properties of space–time discretization methods involving second-order Adams–Bashforth (AB2) method for the solution of one–dimensional (1D) convection equation. It has been established that solving 1D convection equation by three–time level method invokes a numerical or spurious mode, apart from the physical mode (as explained in Sengupta et al., [27]). Here, the long elusive problem of focusing (considered as a problem of non-linear numerical aspect), is shown due to a linear mechanism. The focusing is shown for a wave–packet propagating in a non-periodic domain by a three–time level method. Long time integration shows the physical mode to cause focusing, which shows up as spectacular growth of error–packet(s) at discrete location(s), where the dominant wavenumber (k) depends only on the CFL number (Nc), for the space–time discretization method. The length scale of growing error is independent of wavenumber of the input signal. It is also established that focusing is related to numerical absolute instability, for which the numerical group velocity (VgN1) of the physical mode is zero. However, interestingly, when a compact filter is used, the focusing phenomenon is converted from absolute to convective numerical instability. This brings new insight and satisfactory explanation of focusing and its dependence on the choice of numerical methods and use of filter. As a demonstration of the focusing phenomenon for AB2 method, we use it with a well known combined compact differencing scheme to solve Navier–Stokes equation in a square lid driven cavity for a super-critical post–Hopf bifurcation Reynolds number of 10,000 (based on the side of the cavity and the constant lid velocity). Contrary to the well-established solution with polygonal vortices in the literature, here the solution breaks down after a finite time due to focusing.
Tapan Sengupta, Pierre Sagaut, Aditi Sengupta, Kumar Saurabh. Global spectral analysis of three-time level integration schemes: Focusing phenomenon. Computers & Fluids, Elsevier, 2017, 157, pp.182 - 195. 〈10.1016/j.compfluid.2017.08.033〉. 〈hal-01702350〉
A novel implicit immersed boundary method of high accuracy and efficiency is presented for the simulation of incompressible viscous flow over complex stationary or moving solid boundaries. A boundary force is often introduced in many immersed boundary methods to mimic the presence of solid boundary, such that the overall simulation can be performed on a simple Cartesian grid. The current method inherits this idea and considers the boundary force as a Lagrange multiplier to enforce the no-slip constraint at the solid boundary, instead of applying constitutional relations for rigid bodies. Hence excessive constraint on the time step is circumvented, and the time step only depends on the discretization of fluid Navier-Stokes equations, like the CFL condition in present work. To determine the boundary force, an additional moving force equation is derived. The dimension of this derived system is proportional to the number of Lagrangian points describing the solid boundaries, which makes the method very suitable for moving boundary problems since the time for matrix update and system solving is not significant. The force coefficient matrix is made symmetric and positive definite so that the conjugate gradient method can solve the system quickly. The proposed immersed boundary method is incorporated into the fluid solver with a second-order accurate projection method as a plug-in. The overall scheme is handled under an efficient fractional step framework, namely, prediction, forcing, and projection. Various simulations are performed to validate current method, and the results compare well with previous experimental and numerical studies.
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Moving immersed boundary method. International Journal for Numerical Methods in Fluids, Wiley, 2017, 85 (5), pp.288 - 323. 〈10.1002/fld.4382〉. 〈hal-01592822〉
Journal: International Journal for Numerical Methods in Fluids
V. Mons, Luca Margheri, J.-C. Chassaing, Pierre Sagaut. Data assimilation-based reconstruction of urban pollutant release characteristics. Journal of Wind Engineering and Industrial Aerodynamics, Elsevier, 2017, 169, pp.232 - 250. 〈10.1016/j.jweia.2017.07.007〉. 〈hal-01631036〉 Plus de détails...
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〉 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〉
Christophe Coreixas, Gauthier Wissocq, Guillaume Puigt, Jean-François Boussuge, Pierre Sagaut. Recursive regularization step for high-order lattice Boltzmann methods. Physical Review E , American Physical Society (APS), 2017, 96 (3), pp.033306. 〈10.1103/PhysRevE.96.033306〉. 〈hal-01596322〉 Plus de détails...
A lattice Boltzmann method (LBM) with enhanced stability and accuracy is presented for various Hermite tensor-based lattice structures. The collision operator relies on a regularization step, which is here improved through a recursive computation of nonequilibrium Hermite polynomial coefficients. In addition to the reduced computational cost of this procedure with respect to the standard one, the recursive step allows to considerably enhance the stability and accuracy of the numerical scheme by properly filtering out second-(and higher-) order nonhydrodynamic contributions in under-resolved conditions. This is first shown in the isothermal case where the simulation of the doubly periodic shear layer is performed with a Reynolds number ranging from 104 to 10(6), and where a thorough analysis of the case at Re = 3 x 10(4) is conducted. In the latter, results obtained using both regularization steps are compared against the Bhatnagar-Gross-Krook LBM for standard (D2Q9) and high-order (D2V17 and D2V37) lattice structures, confirming the tremendous increase of stability range of the proposed approach. Further comparisons on thermal and fully compressible flows, using the general extension of this procedure, are then conducted through the numerical simulation of Sod shock tubes with the D2V37 lattice. They confirm the stability increase induced by the recursive approach as compared with the standard one.
Christophe Coreixas, Gauthier Wissocq, Guillaume Puigt, Jean-François Boussuge, Pierre Sagaut. Recursive regularization step for high-order lattice Boltzmann methods. Physical Review E , American Physical Society (APS), 2017, 96 (3), pp.033306. 〈10.1103/PhysRevE.96.033306〉. 〈hal-01596322〉
Olivier Lafforgue, N. Bouguerra, Sebastien Poncet, Isabelle Seyssiecq, Julien Favier, et al.. Thermo-physical properties of synthetic mucus for the study of airway clearance. Journal of Biomedical Materials Research Part A, Wiley, 2017, 105 (11), pp.3025-3033 〈10.1002/jbm.a.36161〉. 〈hal-01596484〉 Plus de détails...
In this article, dynamic viscosity, surface tension, density, heat capacity and thermal conductivity, of a bronchial mucus simulant proposed by Zahm et al., Eur Respir J 1991; 4: 311–315 were experiementally determined. This simulant is mainly composed of a galactomannan gum and a scleroglucan. It was shown that thermophysical properties of synthetic mucus are dependant of scleroglucan concentrations. More importantly and for some scleroglucan concentrations, the syntetic mucus, exhibits, somehow, comparable thermophysical properties to real bronchial mucus. An insight on the microstructure of this simulant is proposed and the different properties enounced previously have been measured for various scleroglucan concentrations and over a certain range of operating temperatures. This synthetic mucus is found to mimic well the rheological behavior and the surface tension of real mucus for different pathologies. Density and thermal properties have been measured for the first time.
Olivier Lafforgue, N. Bouguerra, Sebastien Poncet, Isabelle Seyssiecq, Julien Favier, et al.. Thermo-physical properties of synthetic mucus for the study of airway clearance. Journal of Biomedical Materials Research Part A, Wiley, 2017, 105 (11), pp.3025-3033 〈10.1002/jbm.a.36161〉. 〈hal-01596484〉
Journal: Journal of Biomedical Materials Research Part A
Sylvain Chateau, Julien Favier, Umberto D’ortona, Sebastien Poncet. Transport efficiency of metachronal waves in 3D cilium arrays immersed in a two-phase flow. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 824, pp.931 - 961. 〈10.1017/jfm.2017.352〉. 〈hal-01592834〉 Plus de détails...
This work reports the formation and characterization of antipleptic and symplectic metachronal waves in 3D cilium arrays immersed in a two-fluid environment, with a viscosity ratio of 20. A coupled lattice Boltzmann-immersed-boundary solver is used. The periciliary layer is confined between the epithelial surface and the mucus. Its thickness is chosen such that the tips of the cilia can penetrate the mucus. A purely hydrodynamical feedback of the fluid is taken into account and a coupling parameter alpha is introduced, which allows tuning of both the direction of the wave propagation and the strength of the fluid feedback. A comparative study of both antipleptic and symplectic waves, mapping a cilium interspacing ranging from 1.67 up to 5 cilium lengths, is performed by imposing metachrony. Antipleptic waves are found to systematically outperform symplectic waves. They are shown to be more efficient for transporting and mixing the fluids, while spending less energy than symplectic, random or synchronized motions.
Sylvain Chateau, Julien Favier, Umberto D’ortona, Sebastien Poncet. Transport efficiency of metachronal waves in 3D cilium arrays immersed in a two-phase flow. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 824, pp.931 - 961. 〈10.1017/jfm.2017.352〉. 〈hal-01592834〉
Denis Martinand, Eric Serre, Richard M. Lueptow. Linear and weakly nonlinear analyses of cylindrical Couette flow with axial and radial flows. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 824, pp.438 - 476. 〈10.1017/jfm.2017.351〉. 〈hal-01592948〉 Plus de détails...
Extending previous linear stability analyses of the instabilities developing in permeable Taylor-Couette-Poiseuille flows where axial and radial throughflows are superimposed on the usual Taylor-Couette flow, we further examine the linear behaviour and expand the analysis to consider the weakly nonlinear behaviour of convective-type instabilities by means of the derivation of the fifth-order amplitude equation together with direct numerical simulations. Special attention is paid to the influence of the radius ratio eta = r(in)/r(out), and particularly to wide gaps (small eta) and how they magnify the effects of the radial flow. The instabilities take the form of pairs of counter-rotating toroidal vortices superseded by helical ones as the axial flow is increased. Increasing the radial inflow draws these vortices near the inner cylinder, where they shrink relative to the annular gap, when this gap is wide. Strong axial and radial flows in a narrow annular gap lead to a very large azimuthal wavenumber with steeply sloped helical vortices. Strong radial outflow in a wide annular gap results in very large helical vortices. The analytical and numerical saturated vortices match quite well. In addition, radial inflows or outflows can turn the usually supercritical bifurcation from laminar to vortical flow into a subcritical one. The radial flow above which this change occurs decreases as the radius ratio eta decreases. A practical motivation for this weakly nonlinear analysis is found in modelling dynamic filtration devices, which rely on vortical instabilities to reduce the processes of accumulation on their membranes.
Denis Martinand, Eric Serre, Richard M. Lueptow. Linear and weakly nonlinear analyses of cylindrical Couette flow with axial and radial flows. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 824, pp.438 - 476. 〈10.1017/jfm.2017.351〉. 〈hal-01592948〉
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.931 - 934. 〈10.1016/j.nme.2017.02.007〉. 〈hal-01702229〉 Plus de détails...
Transport codes are the main workhorses for global edge studies and modern divertor design. These tools do not resolve turbulent fluctuations responsible for the bulk of cross-field transport in the Scrape-off Layer (SOL), and solve mean field equations instead. Turbulent fluxes are modelled by diffusive transport along the gradients of the mean fields. Improvements of this description, on the basis of approaches developed in computational fluid dynamics are discussed, broadening the outlook given in Bufferand et al. (2016) [10]. This contribution focuses on additional closure issues related to non-linearities in sources/sinks from plasma-wall interactions, here sputtered fluxes from the plasma facing components. “Fluctuation dressed” sputtering yields Yeff are introduced and calculated from turbulence simulations. Properly taking fluctuations into account is shown to lead to higher sputtering at sub-threshold energies compared to mean field predictions. As a first step towards an implementation in a transport code, the possibility of parametrizing Yeff in terms of the mean fields is tentatively investigated.
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.931 - 934. 〈10.1016/j.nme.2017.02.007〉. 〈hal-01702229〉
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.1171 - 1177. 〈10.1016/j.nme.2016.12.022〉. 〈hal-01702267〉 Plus de détails...
Motivated by Radio Frequency (RF) heating studies, the response of the plasma of tokamaks to the presence of a locally polarized limiter is studied. In a first part, we use the TOKAM3X 3D global edge turbulence code to analyse the impact of such biasing in a realistic geometry. Key features of experimental observations are qualitatively recovered, especially the extension of a potential and density perturbation on long, but finite, distances along connected field lines. The perturbation is also found to extend in the transverse direction. Both observations demonstrate the influence of perpendicular current loops on the plasma confirming the need for an accurate description in reduced models. In a second part, we use the TOKAM2D slab turbulence code to determine the validity of using a transverse Ohm's law for this purpose. Results indicate that a local Ohm's law with a constant and uniform perpendicular resistivity appears at least as an oversimplified description of perpendicular charge transport in a turbulent Scrape-Off Layer.
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.1171 - 1177. 〈10.1016/j.nme.2016.12.022〉. 〈hal-01702267〉
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.187 - 192. 〈10.1016/j.nme.2016.12.025〉. 〈hal-01702237〉 Plus de détails...
Simulations of WEST H-mode divertor scenarios have been performed with SOLEDGE2D-EIRENE edge plasma transport code, both for pure deuterium and nitrogen seeded discharge. In the pure deuterium case, a target heat flux of 8 MW/m2 is reached, but misalignment between heat and the particle outflux yields 50 eV plasma temperature at the target plates. With nitrogen seeding, the heat and particle outflux are observed to be aligned so that lower plasma temperatures at the target plates are achieved together with the required high heat fluxes. This change in heat and particle outflux alignment is analysed with respect to the role of divertor geometry and the impact of vertical vs horizontal target plates on neutrals spreading.
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.187 - 192. 〈10.1016/j.nme.2016.12.025〉. 〈hal-01702237〉
Eddy Constant, Julien Favier, Marcello Meldi, Philippe Meliga, Eric Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers and Fluids, Elsevier, 2017, 157, pp.55 - 72. 〈10.1016/j.compfluid.2017.08.001〉. 〈hal-01591562〉 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.
Eddy Constant, Julien Favier, Marcello Meldi, Philippe Meliga, Eric Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers and Fluids, Elsevier, 2017, 157, pp.55 - 72. 〈10.1016/j.compfluid.2017.08.001〉. 〈hal-01591562〉
Félix Gendre, Denis Ricot, Guillaume Fritz, Pierre Sagaut. Grid refinement for aeroacoustics in the lattice Boltzmann method: A directional splitting approach. Physical Review E , American Physical Society (APS), 2017, 96 (2), pp.023311. 〈10.1103/PhysRevE.96.023311〉. 〈hal-01596329〉 Plus de détails...
This study focuses on grid refinement techniques for the direct simulation of aeroacoustics, when using weakly compressible lattice Boltzmann models, such as the D3Q19 athermal velocity set. When it comes to direct noise computation, very small errors on the density or pressure field may have great negative consequences. Even strong acoustic density fluctuations have indeed a clearly lower amplitude than the hydrodynamic ones. This work deals with such very weak spurious fluctuations that emerge when a vortical structure crosses a refinement interface, which may contaminate the resulting aeroacoustic field. We show through an extensive literature review that, within the framework described above, this issue has never been addressed before. To tackle this problem, we develop an alternative algorithm and compare its behavior to a classical one, which fits our in-house vertex-centered data structure. Our main idea relies on a directional splitting of the continuous discrete velocity Boltzmann equation, followed by an integration over specific characteristics. This method can be seen as a specific coupling between finite difference and lattice Boltzmann, locally on the interface between the two grids. The method is assessed considering two cases: an acoustic pulse and a convected vortex. We show how very small errors on the density field arise and propagate throughout the domain when a vortical flow crosses the refinement interface. We also show that an increased free stream Mach number (but still within the weakly compressible regime) strongly deteriorates the situation, although the magnitude of the errors may remain negligible for purely aerodynamic studies. A drastically reduced level of error for the near-field spurious noise is obtained with our approach, especially for under-resolved simulations, a situation that is crucial for industrial applications. Thus, the vortex case is proved useful for aeroacoustic validations of any grid refinement algorithm.
Félix Gendre, Denis Ricot, Guillaume Fritz, Pierre Sagaut. Grid refinement for aeroacoustics in the lattice Boltzmann method: A directional splitting approach. Physical Review E , American Physical Society (APS), 2017, 96 (2), pp.023311. 〈10.1103/PhysRevE.96.023311〉. 〈hal-01596329〉
H. Bufferand, C. Baudoin, J. Bucalossi, G. Ciraolo, J. Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D–EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.852 - 857. 〈10.1016/j.nme.2016.11.031〉. 〈hal-01702275〉 Plus de détails...
In order to improve cross-field transport description, drifts and currents have been implemented in SOLEDGE2D–EIRENE. The derivation of an equation for the electric potential is recalled. The resolution of current equation is tested in a simple slab case. WEST divertor simulations in forward-B and reverse-B fields are also discussed. A significant increase of ExB shear is observed in the forward-B configuration that could explain a favorable L-H transition in this case.
H. Bufferand, C. Baudoin, J. Bucalossi, G. Ciraolo, J. Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D–EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.852 - 857. 〈10.1016/j.nme.2016.11.031〉. 〈hal-01702275〉
W.A. Gracias, P. Tamain, Eric Serre, R.A. Pitts, L. Garcia. The impact of magnetic shear on the dynamics of a seeded 3D filament in slab geometry. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.798 - 807. 〈10.1016/j.nme.2017.02.022〉. 〈hal-01702187〉 Plus de détails...
Seeded filament simulations are used to study blob dynamics with the state-of-the-art TOKAM3X fluid code in the scrape-off layer (SOL) using a slab geometry. The filamentary dynamics recovered with the code are compared with previously predicted analytical blob velocity scalings while also studying the effect of field line pitch angle on these dynamics and are found to be similar. The effect of changing magnetic topology on filamentary motion is also investigated. Magnetic shear is introduced in the model by the sudden and localised variation of field line pitch angle for a narrow radially located region constituting effectively a shearing zone. Three such shear zones are tested to see how they affect filament motion. Filaments are initialised radially upstream from the shear zone and recorded as they convect towards the far-SOL side. The lowest intensity shear zone allows many of the higher amplitude filaments to pass through after dampening them. On the other hand, the highest intensity shear zones prevent all filaments from progressing to the wall beyond the shear zone and, in certain cases for high density amplitude filaments, is able to generate a new filament downstream from the shear zone.
W.A. Gracias, P. Tamain, Eric Serre, R.A. Pitts, L. Garcia. The impact of magnetic shear on the dynamics of a seeded 3D filament in slab geometry. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.798 - 807. 〈10.1016/j.nme.2017.02.022〉. 〈hal-01702187〉
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.953 - 958. 〈10.1016/j.nme.2017.01.008〉. 〈hal-01702255〉 Plus de détails...
The flux expansion effect on the Scrape-Off Layer equilibrium is inspected through TOKAM3X 3D turbulence simulations. Three magnetic equilibria with analytically controlled flux expansion are built, representing respectively a positive, a null and a negative Shafranov shift. Turbulent E × B fluxes across flux surfaces show similar amplitudes and poloidal distributions in all cases. The ballooning nature of the interchange instability is recovered, with an enhancement of turbulence in the vicinity of the limiter, probably due to a Kelvin–Helmoltz instability. Interestingly, the poloidally averaged density decay length is found to be shorter almost by a factor 2 in the case of flux surfaces compressed at the low-field side midplane, with respect to the opposite case, indicating the presence of unfavorable conditions for the turbulent transport. The difference in the magnetic field line shape is pointed out as a mechanism which affects the turbulent transport across the flux surfaces. Indeed the unstable region has a larger parallel extension when flux expansion in the low-field side is larger. Moreover, the configuration with a lower magnetic shear at the low-field side midplane shows a more unstable behavior. The role of this parameter in turbulence stabilization is qualitatively evaluated. The difference in the distribution of transport along the parallel direction is shown to affect also the parallel flows, which are analyzed for the three proposed cases.
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.953 - 958. 〈10.1016/j.nme.2017.01.008〉. 〈hal-01702255〉
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〉 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〉
Philippe Meliga. Computing the sensitivity of drag and lift in flow past a circular cylinder: Time-stepping versus self-consistent analysis. Physical Review Fluids, American Physical Society, 2017, 2 (7), pp.073905. 〈10.1103/PhysRevFluids.2.073905〉. 〈hal-01698605〉 Plus de détails...
We provide in-depth scrutiny of two methods making use of adjoint-based gradients to compute the sensitivity of drag in the two-dimensional, periodic flow past a circular cylinder (Re≲189): first, the time-stepping analysis used in Meliga et al. [Phys. Fluids 26, 104101 (2014)] that relies on classical Navier-Stokes modeling and determines the sensitivity to any generic control force from time-dependent adjoint equations marched backwards in time; and, second, a self-consistent approach building on the model of Mantič-Lugo et al. [Phys. Rev. Lett. 113, 084501 (2014)] to compute semilinear approximations of the sensitivity to the mean and fluctuating components of the force. Both approaches are applied to open-loop control by a small secondary cylinder and allow identifying the sensitive regions without knowledge of the controlled states. The theoretical predictions obtained by time-stepping analysis reproduce well the results obtained by direct numerical simulation of the two-cylinder system. So do the predictions obtained by self-consistent analysis, which corroborates the relevance of the approach as a guideline for efficient and systematic control design in the attempt to reduce drag, even though the Reynolds number is not close to the instability threshold and the oscillation amplitude is not small. This is because, unlike simpler approaches relying on linear stability analysis to predict the main features of the flow unsteadiness, the semilinear framework encompasses rigorously the effect of the control on the mean flow, as well as on the finite-amplitude fluctuation that feeds back nonlinearly onto the mean flow via the formation of Reynolds stresses. Such results are especially promising as the self-consistent approach determines the sensitivity from time-independent equations that can be solved iteratively, which makes it generally less computationally demanding. We ultimately discuss the extent to which relevant information can be gained from a hybrid modeling computing self-consistent sensitivities from the postprocessing of DNS data. Application to alternative control objectives such as increasing the lift and alleviating the fluctuating drag and lift is also discussed.
Philippe Meliga. Computing the sensitivity of drag and lift in flow past a circular cylinder: Time-stepping versus self-consistent analysis. Physical Review Fluids, American Physical Society, 2017, 2 (7), pp.073905. 〈10.1103/PhysRevFluids.2.073905〉. 〈hal-01698605〉
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〉 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〉
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Thermal effects of substrate on Marangoni flow in droplet evaporation: Response surface and sensitivity analysis. International Journal of Heat and Mass Transfer, Elsevier, 2017, 113, pp.354 - 365. 〈10.1016/j.ijheatmasstransfer.2017.05.076〉. 〈hal-01532757〉 Plus de détails...
In this paper, the evaporation of sessile droplets resting on a substrate with different thermal properties is numerically investigated. Computations are based on a transient axisymmetric numerical model. Special attention is paid to evaluate thermal effects of substrate on the structure of bulk fluid flow in the course of evaporation. Numerical results reveal that Marangoni convection induced by non-uniform distribution of temperature along the interface exhibits three distinctly different behaviours: inward flow, multicellular flow and outward flow, consequently resulting in different particle depositions. It is highlighted that three factors (i.e. relative thermal conductivity, relative substrate thickness and relative substrate temperature) strongly affect the flow pattern. In order to further investigate the coupling effects of different influential factors, a Kriging-based response surface method is introduced. We model the flow behaviour as a function of continuous influential factors using a limited number of computations corresponding to discrete values of the inputs. The sensitivities of the Marangoni flow are also analysed using Sobol’ index to study the coupling mechanisms of influential factors. The proposed method can be used to forecast the flow patterns for any input parameter without additional sophisticated computer simulation, and allows to confidently estimate an unknown environmental parameter.
Xue Chen, Xun Wang, Paul G. Chen, Qiusheng Liu. Thermal effects of substrate on Marangoni flow in droplet evaporation: Response surface and sensitivity analysis. International Journal of Heat and Mass Transfer, Elsevier, 2017, 113, pp.354 - 365. 〈10.1016/j.ijheatmasstransfer.2017.05.076〉. 〈hal-01532757〉
Journal: International Journal of Heat and Mass Transfer
Alistair Revell, Joseph O’connor, Abhishek Sarkar, Cuicui Li, Julien Favier, et al.. The PELskin project: part II—investigating the physical coupling between flexible filaments in an oscillating flow. Meccanica, Springer Verlag, 2017, 52 (8), pp.1781 - 1795. 〈10.1007/s11012-016-0525-9〉. 〈hal-01592870〉 Plus de détails...
The fluid-structure interaction mechanisms of a coating composed of flexible flaps immersed in a periodically oscillating channel flow is here studied by means of numerical simulation, employing the Euler-Bernoulli equations to account for the flexibility of the structures. A set of passively actuated flaps have previously been demonstrated to deliver favourable aerodynamic impact when attached to a bluff body undergoing periodic vortex shedding. As such, the present configuration is identified to provide a useful test-bed to better understand this mechanism, thought to be linked to experimentally observed travelling waves. Having previously validated and elucidated the flow mechanism in Paper 1 of this series, we hereby undertake a more detailed analysis of spectra obtained for different natural frequency of structures and different configurations, in order to better characterize the mechanisms involved in the organized motion of the structures. Herein, this wave-like behaviour, observed at the tips of flexible structures via interaction with the fluid flow, is characterized by examining the time history of the filaments motion and the corresponding effects on the fluid flow, in terms of dynamics and frequency of the fluid velocity. Results indicate that the wave motion behaviour is associated with the formation of vortices in the gaps between the flaps, which itself are a function of the structural resistance to the cross flow. In addition, formation of vortices upstream of the leading and downstream of the trailing flap is seen, which interact with the formation of the shear-layer on top of the row. This leads to a phase shift in the wave-type motion along the row that resembles the observation in the cylinder case.
Alistair Revell, Joseph O’connor, Abhishek Sarkar, Cuicui Li, Julien Favier, et al.. The PELskin project: part II—investigating the physical coupling between flexible filaments in an oscillating flow. Meccanica, Springer Verlag, 2017, 52 (8), pp.1781 - 1795. 〈10.1007/s11012-016-0525-9〉. 〈hal-01592870〉
Julien Favier, Cuicui Li, Laura Kamps, Alistair Revell, Joseph O’connor, et al.. The PELskin project—part I: fluid–structure interaction for a row of flexible flaps: a reference study in oscillating channel flow. Meccanica, Springer Verlag, 2017, 52 (8), pp.1767 - 1780. 〈10.1007/s11012-016-0521-0〉. 〈hal-01592866〉 Plus de détails...
Previous studies of flexible flaps attached to the aft part of a cylinder have demonstrated a favourable effect on the drag and lift force fluctuation. This observation is thought to be linked to the excitation of travelling waves along the flaps and as a consequence of that, periodic shedding of the von Karman vortices is altered in phase. A more general case of such interaction is studied herein for a limited row of flaps in an oscillating flow; representative of the cylinder case since the transversal flow in the wake-region shows oscillating character. This reference case is chosen to qualify recently developed numerical methods for the simulation of fluid-structure interaction in the context of the EU funded 'PELskin' project. The simulation of the two-way coupled dynamics of the flexible elements is achieved via a structure model for the flap motion, which was implemented and coupled to two different fluid solvers via the immersed boundary method. The results show the waving behaviour observed at the tips of the flexible elements in interaction with the fluid flow and the formation of vortices in the gaps between the flaps. In addition, formation of vortices upstream of the leading and downstream of the trailing flap is seen, which interact with the formation of the shear-layer on top of the row. This leads to a phase shift in the wave-type motion along the row that resembles the observation in the cylinder case.
Julien Favier, Cuicui Li, Laura Kamps, Alistair Revell, Joseph O’connor, et al.. The PELskin project—part I: fluid–structure interaction for a row of flexible flaps: a reference study in oscillating channel flow. Meccanica, Springer Verlag, 2017, 52 (8), pp.1767 - 1780. 〈10.1007/s11012-016-0521-0〉. 〈hal-01592866〉
Alekseenko Elena, Bernard Roux. Submerged Aquatic Vegetation Restoration in Brackish Ecosystems Subject to Strong Winds and Coastal Jets. Oceanography & Fisheries Open access Journal, 2017, 2 (4), pp.555595. 〈10.19080/OFOAJ.2017.02.555595〉. 〈hal-01813859〉 Plus de détails...
The bottom shear stress (BSS) in a windy Mediterranean lagoon has been carefully investigated through numerical modelling. BSS maps have been obtained for the entire lagoon. The aim is to compare BSS with its critical value in the near shoreareas selected for SAV replanting which are subject to downwind coastal jets.
Alekseenko Elena, Bernard Roux. Submerged Aquatic Vegetation Restoration in Brackish Ecosystems Subject to Strong Winds and Coastal Jets. Oceanography & Fisheries Open access Journal, 2017, 2 (4), pp.555595. 〈10.19080/OFOAJ.2017.02.555595〉. 〈hal-01813859〉
Journal: Oceanography & Fisheries Open access Journal
Marcello 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〉 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.
Marcello 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〉
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〉
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〉 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〉
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〉 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〉
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, IOP Publishing, 2017, 57 (3), pp.036029. 〈10.1088/1741-4326/aa5332〉. 〈hal-01592945〉 Plus de détails...
The poloidal asymmetries of parallel flows in edge plasmas are investigated by the 3D fluid turbulence code TOKAM3X. A diverted COMPASS-like magnetic equilibrium is used for the simulations. The measurements and simulations of parallel Mach numbers are compared, and exhibit good qualitative agreement. Small-scale turbulent transport is observed to dominate near the low field side midplane, even though it co-exists with significant large-scale cross-field fluxes. Despite the turbulent nature of the plasma in the divertor region, simulations show the low effectiveness of turbulence for the cross-field transport towards the private flux region. Nevertheless, a complex pattern of fluxes associated with the average field components are found to cross the separatrix in the divertor region. Large-scale and small-scale turbulent E x B transport, along with the del B drift, drive the asymmetries in parallel flows. A semian-alytical model based on mass and parallel momentum balances allows the poloidal drift effects on the asymmetry pattern to be evaluated. As in the experiments, a reversed B-T simulation provides a way of self-consistently separating the effects of turbulent transport and large-scale flows, which must be reversed for a reversed field. The large-scale contribution is found to be responsible for typically 50% of the effect on the Mach number, evaluated at the top of the machine. The presented picture shows the complex interplay between drifts and turbulence, underlining the necessity of a global approach to edge plasma modelling, including a self-consistent description of the turbulence.
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, IOP Publishing, 2017, 57 (3), pp.036029. 〈10.1088/1741-4326/aa5332〉. 〈hal-01592945〉
A novel immersed boundary method is introduced for simulating the fluid-structure interaction problem. Unlike the body-conforming mesh method which imposes the no-slip boundary conditions directly on the immersed interface, the immersed boundary method adopts a boundary force for the presence of the immersed solid. Therefore, the fluid is simply simulated on a fixed Cartesian mesh irrespective the movement of the immersed solid, which circumvents the mesh quality issue that frequently happens in the body-conforming mesh method. To enforce the correct boundary condition, we derive an additional moving force equation. This additional equation is integrated into a second order accurate fractional step method and solved with the conjugate gradient method. The proposed method is validated with several one-way fluid-structure interaction examples.
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Implicit immersed boundary method for fluid-structure interaction. La Houille Blanche - Revue internationale de l'eau, EDP Sciences, 2017, 1/2017 (1), pp.33 - 36. 〈10.1051/lhb/2017005〉. 〈hal-01592851〉
Journal: La Houille Blanche - Revue internationale de l'eau
R.J.A. Howard, Eric Serre. Large eddy simulation in Code_Saturne of thermal mixing in a T junction with brass walls. International Journal of Heat and Fluid Flow, Elsevier, 2017, 63, pp.119 - 127. 〈10.1016/j.ijheatfluidflow.2016.09.011〉. 〈hal-01592931〉 Plus de détails...
Following on from Kuhn et al (2010) we study the capability of large eddy simulation with conjugate heat transfer to predict thermal fluctuations with thermal mixing. Wall functions are used to model the wall heat transfer. Comparison with experimental results show that the temperature variance on the outer skin of the solid is well predicted by the simulation. It is shown that the variance of thermal flux in the fluid closely maps the temperature variance at the outer boundary of the solid. Since the variance of thermal flux is closely related to the dissipation of temperature variance it can be concluded that the dissipation of temperature variance in the fluid is linked to temperature variance in the solid. Analysis of the equation of the temperature variance in the solid confirms this is indeed the case. It is the dissipation of temperature variance in the fluid that characterizes how the temperature variance penetrates the solid. Thus RANS modelling can be used to predict thermal variance in solids provided that there is an accurate model for the dissipation of temperature variance at the wall and an equation for the thermal variance in the solid is solved.
R.J.A. Howard, Eric Serre. Large eddy simulation in Code_Saturne of thermal mixing in a T junction with brass walls. International Journal of Heat and Fluid Flow, Elsevier, 2017, 63, pp.119 - 127. 〈10.1016/j.ijheatfluidflow.2016.09.011〉. 〈hal-01592931〉
Journal: International Journal of Heat and Fluid Flow
E Alekseenko, B Roux, D Fougere, Paul G. Chen. The effect of wind induced bottom shear stress and salinity on Zostera noltii replanting in a Mediterranean coastal lagoon. Estuarine, Coastal and Shelf Science, Elsevier, 2017, 187, pp.293-305. 〈10.1016/j.ecss.2017.01.010〉. 〈hal-01453377〉 Plus de détails...
The paper concerns the wind influence on bottom shear stress and salinity levels in a Mediterranean semi-enclosed coastal lagoon (Etang de Berre), with respect to a replanting program of Zostera noltii . The MARS3D numerical model is used to analyze the 3D current, salinity and temperature distribution induced by three meteorological, oceanic and anthropogenic forcings in this lagoon. The numerical model has been carefully validated by comparison with daily observations of the vertical salinity and temperature profiles at three mooring stations, for one year. Then, two modelling scenarios are considered. The first scenario (scen.## 1), starting with an homogeneous salinity of S = 20 PSU and without wind forcing, studies a stratification process under the influence of a periodic seawater inflow and a strong freshwater inflow from an hydropower plant (250 m3/s). Then, in the second scenario (scen.## 2), we study how a strong wind of 80 km/h can mix the haline stratification obtained at the end of scen.## 1. The most interesting results concern four nearshore replanting areas; two are situated on the eastern side of EB and two on the western side. The results of scen.## 2 show that all these areas are subject to a downwind coastal jet. Concerning bottom salinity, the destratification process is very beneficial; it always remains greater than 12 PSU for a N-NW wind of 80 km/h and an hydropower runoff of 250 m3/s. Special attention is devoted to the bottom shear stress (BSS) for different values of the bottom roughness parameter (for gravels, sands and silts), and to the bottom salinity. Concerning BSS, it presents a maximum near the shoreline and decreases along transects perpendicular to the shoreline. There exists a zone, parallel to the shoreline, where BSS presents a minimum (close to zero). When comparing the BSS value at the four replanting areas with the critical value, BSScr, at which the sediment mobility would occur, we see that for the smaller roughness values (ranging from z0 = 3.5 × 10-4 mm, to 3.5 × 10-2 mm) BSS largely surpasses this critical value. For a N-NW wind speed of 40 km/h (which is blowing for around 100 days per year), BSS still largely surpasses BSScr - at least for the silt sediments (ranging from z0 = 3.5 × 10-4 mm, to 3.5 × 10-3 mm). This confirms the possibility that the coastal jet could generate sediment mobility which could have a negative impact for SAV replanting.
E Alekseenko, B Roux, D Fougere, Paul G. Chen. The effect of wind induced bottom shear stress and salinity on Zostera noltii replanting in a Mediterranean coastal lagoon. Estuarine, Coastal and Shelf Science, Elsevier, 2017, 187, pp.293-305. 〈10.1016/j.ecss.2017.01.010〉. 〈hal-01453377〉
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〉 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〉
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, In press. 〈hal-01655295〉 Plus de détails...
The nonlocal expression proposed by Luciani-Mora-Virmont is implemented into a 1D fluid model for the scrape-off layer. Analytic solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The nonlocal heat flux is compared to Spitzer-Härm heat flux for different collisionality.
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, In press. 〈hal-01655295〉
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〉 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〉
X. Litaudon, S. Abduallev, M. Abhangi, P. Abreu, M. Afzal, et al.. Overview of the JET results in support to ITER. Nuclear Fusion, IOP Publishing, 2017, 57 (10), pp.102001. 〈hal-01660974〉 Plus de détails...
The 2014-2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L-H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at beta(N) similar to 1.8 and n/n(GW) similar to 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D-T campaign and 14 MeV neutron calibration strategy are reviewed.
X. Litaudon, S. Abduallev, M. Abhangi, P. Abreu, M. Afzal, et al.. Overview of the JET results in support to ITER. Nuclear Fusion, IOP Publishing, 2017, 57 (10), pp.102001. 〈hal-01660974〉
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〉 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), 〈10.1088/0169-5983/48/6/061401〉. 〈hal-01461792〉 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. 〈10.1016/j.jcp.2016.07.036〉. 〈hal-01461789〉 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〉
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, Elsevier, 2016, 117, pp.203-218. 〈10.1016/j.supflu.2016.06.020〉. 〈hal-01369830〉 Plus de détails...
In this study, adsorption in a model binary mixture is investigated near the critical point in a side-heated cavity. The diverging behavior of the equilibrium constant and the Piston effect are taken into account and their influence on the adsorption process is pointed to. The modeling is based on numerical integration of the differential equations, considering the Navier-Stokes equations coupled with the energy and mass diffusion balances. By means of this model, the temperature, density and adsorbed concentration profiles are drawn at different times. Some fundamental concepts about the system’s response to the heating are illustrated. The results reveal that the adsorption process is influenced by the combined effect of several parameters, such as the gravity and the proximity to the critical point. In particular, the adsorbed amount exhibits a reversed dependency on the wall heating very close to the critical point, which confirms the complexity of such a process in binary systems near critical conditions.
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, Elsevier, 2016, 117, pp.203-218. 〈10.1016/j.supflu.2016.06.020〉. 〈hal-01369830〉
Romain Oguic, Sébastien Poncet, Stéphane Viazzo. High-order direct numerical simulations of a turbulent round impinging jet onto a rotating heated disk in a highly confined cavity. International Journal of Heat and Fluid Flow, Elsevier, 2016, 61 (B), pp.366-378. 〈10.1016/j.ijheatfluidflow.2016.05.013〉. 〈hal-01461786〉 Plus de détails...
The present work reports Direct Numerical Simulations (DNS) of an impinging round jet onto a rotating heated disk in a confined rotor-stator cavity. The geometrical characteristics of the system correspond to the experimental set-up developed by u. Pelle and S. Harmand. Heat transfer study in a rotor-stator system air-gap with an axial inflow. Applied Thermal Engineering, 29:1532-1543, 2009.]. The aspect ratio of the cavity G = h/R-d between the interdisk spacing h and the rotor radius R-d is fixed to 0.02 corresponding to a narrow-gap cavity. The axial Reynolds number Red based on the jet characteristics is also fixed to Re-j = 5300, while the rotational Reynolds number Re-Omega may vary to preserve the swirl parameter N proportional to Re(Omega)dRe(j) (0 <= N <= 2.47) between the present simulations and the experimental data of [J. Pelle and S. Harmand. Heat transfer study in a rotor-stator system air-gap with an axial inflow. Applied Thermal Engineering, 29:1532-1543, 2009.] and [T. D. Nguyen, J. Pelle, S. Harmand, and S. Poncet. PIV measurements of an air jet impinging on an open rotor-stator system. Experiments in Fluids, 53:401-412, 2012.] for comparisons. The results are discussed in terms of radial distributions of the mean velocity components and corresponding Reynolds stress tensor components. The swirl parameter does not modify the size of the recirculation bubble developed along the stator close to the pipe exit. For N >= 1.237, centrifugal effects at the rotor periphery are balanced by a centripetal flow along the stator. Some spiral patterns develop then in the stator boundary layer corresponding to the SRIII instability of [L. Schouveiler, P. Le Gal, and M. P. Chauve. Instabilities of the flow between a rotating and a stationary disk. Journal of Fluid Mechanics, 443:329-350, 2001.] in an enclosed cavity. The numerical results are found to agree particularly well with the experimental data in terms of the distribution of the local Nusselt number along the rotor. Finally, a correlation for its averaged value is proposed according to the swirl parameter. (C) 2016 Elsevier Inc. All rights reserved.
Romain Oguic, Sébastien Poncet, Stéphane Viazzo. High-order direct numerical simulations of a turbulent round impinging jet onto a rotating heated disk in a highly confined cavity. International Journal of Heat and Fluid Flow, Elsevier, 2016, 61 (B), pp.366-378. 〈10.1016/j.ijheatfluidflow.2016.05.013〉. 〈hal-01461786〉
Journal: International Journal of Heat and Fluid Flow
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〉 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〉
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.575-580. 〈10.1002/ctpp.201610038〉. 〈hal-01455240〉 Plus de détails...
The interplay between Langmuir probes (LP) and Scrape-Off-Layer plasma turbulence is numerically investigated with the TOKAM2D and TOKAM3X fluid codes. The LP is modelled by biasing a part of the target plates surface; we then study its impact on the turbulent transport 1) in presence of electron temperature fluctuations and 2) with a complete description of the parallel dynamics. We find that a biased probe can disturb local plasma parameters as well as turbulent transport in its vicinity, by polarizing the connected flux tube and thus driving a strong ExB vortex. Moreover, electron temperature fluctuations are found to account significantly those of floating potential, but with a limited impact on flux measurements depending on the probe's exact geometry. The 3D study of the problem shows the attenuation, but the persistency, of these perturbations induced by the presence of the LP. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.575-580. 〈10.1002/ctpp.201610038〉. 〈hal-01455240〉
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〉 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〉
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.569-574. 〈10.1002/ctpp.201610063〉. 〈hal-01455242〉 Plus de détails...
The impact of a 3D localized particle source on the edge plasma in 3D global turbulence simulations is investigated using the TOKAM3X fluid code. Results apply to advanced fueling methods such as Supersonic Molecular Beam Injection (SMBI) or pellets injection. The fueling source is imposed as a volumetric particle source in the simulations so that the physics leading to the ionization of particles and its localization are not taken into account. As already observed in experiments, the localized particle source strongly perturbs both turbulence and the large scale organization of the edge plasma. The localized increase of the pressure generated by the source drives sonic parallel flows in the plasma, leading to a poloidal redistribution of the particles on the time scale of the source duration. However, the particle deposition also drives localized transverse pressure gradients which impacts the stability of the plasma with respect to interchange processes. The resulting radial transport occurs on a sufficiently fast time scale to compete with the parallel redistribution of particles, leading to immediate radial losses of a significant proportion of the injected particles. Low Field Side (LFS) and High Field Side (HFS) injections exhibit different dynamics due to their interaction with curvature. In particular, HFS particle deposition drives an inward flux leading to differences in the particle deposition efficiency (higher for HFS than LFS). These results demonstrate the importance of taking into account plasma transport in a self-consistent manner when investigating fueling methods. ((c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.569-574. 〈10.1002/ctpp.201610063〉. 〈hal-01455242〉
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.555-562. 〈10.1002/ctpp.201610033〉. 〈hal-01455239〉 Plus de détails...
Cross-field transport in edge tokamak plasmas is known to be dominated by turbulent transport. A dedicated effort has been made to simulate this turbulent transport from first principle models but the numerical cost to run these simulations on the ITER scale remains prohibitive. Edge plasma transport study relies mostly nowadays on so-called transport codes where the turbulent transport is taken into account using effective ad-hoc diffusion coeffecients. In this contribution, we propose to introduce a transport equation for the turbulence intensity in SOLEDGE2D-EIRENE to describe the interchange turbulence properties. Going beyond the empirical diffusive model, this system automatically generates profiles for the turbulent transport and hence reduces the number of degrees of freedom for edge plasma transport codes. We draw inspiration from the k-epsilon model widely used in the neutral fluid community. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.555-562. 〈10.1002/ctpp.201610033〉. 〈hal-01455239〉
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〉 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, 321, pp.1170-1184. 〈10.1016/j.jcp.2016.06.026〉. 〈hal-01336315〉 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, 321, pp.1170-1184. 〈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. 〈10.1080/14685248.2016.1191641〉. 〈hal-01429646〉 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. 〈10.1016/j.compfluid.2016.03.009〉. 〈hal-01461781〉 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), 〈10.1088/0741-3335/58/4/044005〉. 〈hal-01461784〉 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. 〈10.1175/JAS-D-15-0240.1〉. 〈hal-01461782〉 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. 〈10.1063/1.4943625〉. 〈hal-01428632〉 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〉
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〉 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〉
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〉 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〉
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〉 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〉
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〉 Plus de détails...
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, 〈10.1088/0031-8949/T167/1/014073〉. 〈hal-01459103〉 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〉
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-01276637〉 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.147-182. 〈10.1017/jfm.2015.705 〉. 〈hal-01276637〉
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〉 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〉
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〉 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
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〉
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〉 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〉
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Improved Implicit Immersed Boundary Method via Operator Splitting. Ibrahimbegovic, A. Computational Methods for Solids and Fluids : Multiscale Analysis, Probability Aspects and Model Reduction, 41, pp.49-66, 2016, Computational Methods in Applied Sciences, 〈10.1007/978-3-319-27996-1_3〉. 〈hal-01462069〉 Plus de détails...
We present an implicit immersed boundary method via operator splitting technique for simulating fluid flow over moving solid with complex shape. An additional moving force equation is derived in order to impose the interface velocity condition exactly on the immersed surface. The moving force matrix is formulated to be symmetric and positive definite, thus its calculation is computational inexpensive by using the conjugate gradient method. Moreover, the proposed immersed boundary method is incorporated into the rotational incremental projection method as a plug-in. No numerical boundary layers will be generated towards the velocity and pressure during the calculation. The method is validated through various benchmark tests.
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Improved Implicit Immersed Boundary Method via Operator Splitting. Ibrahimbegovic, A. Computational Methods for Solids and Fluids : Multiscale Analysis, Probability Aspects and Model Reduction, 41, pp.49-66, 2016, Computational Methods in Applied Sciences, 〈10.1007/978-3-319-27996-1_3〉. 〈hal-01462069〉
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〉 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〉
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〉 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〉
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〉 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. 〈10.1016/j.jcp.2015.10.026〉. 〈hal-01225681〉 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〉
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〉 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〉
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〉 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〉
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〉 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. 〈10.1016/j.ijrefrig.2015.07.030〉. 〈hal-01300110〉 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〉
The problem of flapping filaments in an uniform incoming flow is tackled 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 filament flexural rigidity and the tension. The instantaneous wall conditions on the filament are imposed via a system of singular body forces, consistently discretised on the lattice of the Boltzmann equation. We first consider the case of a single beating filament, and then the case of multiple beating filaments in a side-by-side configuration, focussing on the modal behaviour of the whole dynamical systems.
Julien Favier, Alistair Revell, Alfredo Pinelli. Fluid Structure Interaction of Multiple Flapping Filaments Using Lattice Boltzmann and Immersed Boundary Methods. Advances in Fluid-Structure Interaction, 133, Springer, pp.167-178, 2016, Notes on Numerical Fluid Mechanics and Multidisciplinary Design 978-3-319-27384-6. 〈10.1007/978-3-319-27386-0_10〉. 〈hal-01705549〉
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〉 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〉
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〉 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. 〈10.1017/S0022377815001075〉. 〈hal-01299264〉 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〉