Publications de l'équipe Instabilités, Turbulence & Contrôle
2019
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows. Physical Review E , American Physical Society (APS), 2019. ⟨hal-02265484⟩ Plus de détails...
An extended version of the hybrid recursive regularized Lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regu-larized lattice Boltzmann approach well suited for high Reynolds number flows, whereas the energy and humidity related equations are solved by a finite volume approach. Two options are investigated to account for cloud formation in atmospheric flow simulations. The first option considers a single conservation equation for total water and an appropriate invariant variable of temperature. In the other approach, liquid and vapor are considered via two separated equations, and phase transition is accounted for via a relaxation procedure. The obtained models are then systematically validated on four well-established benchmark problems including a double diffusive Rayleigh Bénard convection of humid air, 2D and 3D thermal moist rising bubble under convective atmospheric environment as well as a shallow cumulus convection in framework of large-eddy simulation.
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows. Physical Review E , American Physical Society (APS), 2019. ⟨hal-02265484⟩
G. Farag, Pierre Boivin, P. Sagaut. Interaction of two-dimensional spots with a heat releasing/absorbing shock wave: linear interaction approximation results. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2019, 871, pp.865-895. ⟨10.1017/jfm.2019.324⟩. ⟨hal-02142649⟩ Plus de détails...
The canonical interaction between a two-dimensional weak Gaussian disturbance (en-tropy spot, density spot, weak vortex) with an exothermic/endothermic planar shock wave is studied via the Linear Interaction Approximation. To this end, a unified framework based on an extended Kovasznay decomposition that simultaneously accounts for non-acoustic density disturbances along with a poloidal-toroidal splitting of the vorticity mode and for heat-release is proposed. An extended version of Chu's definition for the energy of disturbances in compressible flows encompassing multi-component mixtures of gases is also proposed. This new definition precludes spurious non-normal phenomena when computing the total energy of extended Kovasznay modes. Detailed results are provided for three cases, along with fully general expressions for mixed solutions that combine incoming vortical, entropy and density disturbances.
G. Farag, Pierre Boivin, P. Sagaut. Interaction of two-dimensional spots with a heat releasing/absorbing shock wave: linear interaction approximation results. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2019, 871, pp.865-895. ⟨10.1017/jfm.2019.324⟩. ⟨hal-02142649⟩
E. Yim, P. Meliga, F. Gallaire. Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Royal Society, The, 2019, 475 (2225), pp.20190018. ⟨10.1098/rspa.2019.0018⟩. ⟨hal-02177032⟩ Plus de détails...
We investigate the saturation of harmonically forced disturbances in the turbulent flow over a backward-facing step subjected to a finite amplitude forcing. The analysis relies on a triple decomposition of the unsteady flow into mean, coherent and incoherent components. The coherent-incoherent interaction is lumped into a Reynolds averaged Navier-Stokes (RANS) eddy viscosity model, and the mean-coherent interaction is analysed via a semi-linear resolvent analysis building on the laminar approach by Mantic-Lugo & Gallaire (2016 J. Fluid Mech. 793, 777-797. (doi:10.1017/jfm.2016.109)). This provides a self-consistent modelling of the interaction between all three components, in the sense that the coherent perturbation structures selected by the resolvent analysis are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations, while also accounting for the effect of the incoherent scale. The model does not require any input from numerical or experimental data, and accurately predicts the saturation of the forced coherent disturbances, as established from comparison to time-averages of unsteady RANS simulation data.
E. Yim, P. Meliga, F. Gallaire. Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Royal Society, The, 2019, 475 (2225), pp.20190018. ⟨10.1098/rspa.2019.0018⟩. ⟨hal-02177032⟩
Journal: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Pierre Magnico. Electro-Kinetic Instability in a Laminar Boundary Layer Next to an Ion Exchange Membrane. International Journal of Molecular Sciences, MDPI, 2019, 20 (10), pp.2393. ⟨10.3390/ijms20102393⟩. ⟨hal-02177052⟩ Plus de détails...
The electro-kinetic instability in a pressure driven shear flow near an ion exchange membrane is considered. The electrochemical system, through which an electrical potential drop is applied, consists in a polarization layer in contact with the membrane and a bulk. The numerical investigation contained two aspects: analysis of the instability modes and description of the Lagrangian transport of fluid and ions. Regarding the first aspect, the modes were analyzed as a function of the potential drop. The analysis revealed how the spatial distribution of forces controls the dynamics of vortex association and dissociation. In particular, the birth of a counter-clockwise vortex between two clockwise vortices, and the initiation of clusters constituting one or two envelopes wrapping a vortex group, were examined. In regards to the second aspect, the trajectories were computed with the fourth order Runge Kutta scheme for the time integration and with the biquadratric upstream scheme for the spatial and time interpolation of the fluid velocity and the ion flux. The results for the periodic mode showed two kinds of trajectories: the trochoidal motion and the longitudinal one coupled with a periodic transverse motion. For the aperiodic modes, other mechanisms appeared, such as ejection from the mixing layer, trapping by a growing vortex or merging vortices. The analysis of the local velocity field, the vortices' shape, the spatial distribution of the forces and the ion flux components explained these trajectories.
Pierre Magnico. Electro-Kinetic Instability in a Laminar Boundary Layer Next to an Ion Exchange Membrane. International Journal of Molecular Sciences, MDPI, 2019, 20 (10), pp.2393. ⟨10.3390/ijms20102393⟩. ⟨hal-02177052⟩
Journal: International Journal of Molecular Sciences
Uwe Ehrenstein. Thrust and drag scaling of a rigid low-aspect-ratio pitching plate. Journal of Fluids and Structures, Elsevier, 2019, 87, pp.39-57. ⟨10.1016/j.jfluidstructs.2019.03.013⟩. ⟨hal-02090856⟩ Plus de détails...
Uwe Ehrenstein. Thrust and drag scaling of a rigid low-aspect-ratio pitching plate. Journal of Fluids and Structures, Elsevier, 2019, 87, pp.39-57. ⟨10.1016/j.jfluidstructs.2019.03.013⟩. ⟨hal-02090856⟩
Giorgio Giorgiani, H. Bufferand, G. Ciraolo, Eric Serre, P. Tamain. A magnetic-field independent approach for strongly anisotropic equations arising plasma-edge transport simulations. Nuclear Materials and Energy, Elsevier, 2019, 19, pp.340-345. ⟨10.1016/j.nme.2019.03.002⟩. ⟨hal-02177048⟩ Plus de détails...
A [Summary] The control of the power exhaust in tokamaks is still an open issue for the future fusion operations. The heat loads on divertor and limiter PFCs is largely determined by the physics of the Scrape-Off Layer (SOL), and therefore it depends mainly on the geometry of the magnetic surfaces and on the geometry of wall components. A better characterization of the heat exhaust mechanisms requires therefore to improve the capabilities of the transport codes in terms of geometrical description of the wall components and in terms of the description of the magnetic geometry. The possibility of dealing with evolving magnetic configurations becomes also critical: during start-up or control operations, for example, the evolution of particles and heat fluxes is little known, although being critical for the safety of the machine. Hence, among the new capabilities of future transport codes will be the possibility of accurately describe the reactor chamber, and the flexibility with respect the magnetic configuration. In particular, avoiding expensive re-meshing of the computational domain in case of evolving equilibrium is mandatory. In order to fulfill these requirements, in this work a fluid solver based on non-aligned discretization is used to solve the plasma-edge transport equations for density, momentum and energies. Preliminary tests on non-structured meshes and realistic geometries/physical parameters show the pertinency of this novel approach.
Giorgio Giorgiani, H. Bufferand, G. Ciraolo, Eric Serre, P. Tamain. A magnetic-field independent approach for strongly anisotropic equations arising plasma-edge transport simulations. Nuclear Materials and Energy, Elsevier, 2019, 19, pp.340-345. ⟨10.1016/j.nme.2019.03.002⟩. ⟨hal-02177048⟩
S. Baschetti, H. Bufferand, G. Ciraolo, N. Fedorczak, P. Ghendrih, et al.. A κ − ε model for plasma anomalous transport in tokamaks: closure via the scaling of the global confinement. Nuclear Materials and Energy, Elsevier, 2019, 19, pp.200-204. ⟨10.1016/j.nme.2019.02.032⟩. ⟨hal-02177039⟩ Plus de détails...
A reduced model for radial anomalous transport of plasma in tokamaks, inspired by the Reynolds-Averaged Navier-Stokes (RANS) approach, is presented assuming diffusion as governing mechanism. In order to self-consistently calculate transport coefficients, an empirical equation is built for the turbulent kinetic energy and the system is closed via the scaling law of global confinement. In such way the SOL width appears to recover experimental dependencies with respect to machine parameters and interestingly, when the model is implemented in a 2D transport code for a realistic study-case, mean fields retrieve some features already observed in 1st-principle turbulent codes.
S. Baschetti, H. Bufferand, G. Ciraolo, N. Fedorczak, P. Ghendrih, et al.. A κ − ε model for plasma anomalous transport in tokamaks: closure via the scaling of the global confinement. Nuclear Materials and Energy, Elsevier, 2019, 19, pp.200-204. ⟨10.1016/j.nme.2019.02.032⟩. ⟨hal-02177039⟩
V.S. Neverov, A.B. Kukushkin, U. Kruezi, M.F. Stamp, H. Weisen, et al.. Determination of isotope ratio in the divertor of JET-ILW by high-resolution H α spectroscopy: H–D experiment and implications for D–T experiment. Nuclear Fusion, IOP Publishing, 2019, 59 (4), pp.046011. ⟨10.1088/1741-4326/ab0000⟩. ⟨hal-02177120⟩ Plus de détails...
The data of the H alpha high-resolution spectroscopy, collected on the multiple lines of sight, which cover the entire divertor space in poloidal cross-section, during the recent hydrogen-deuterium experiments in JET-ILW (ITER-like wall), are processed. A strong spatial inhomogeneity of the hydrogen concentration, H/(H + D), in divertor is found in many pulses. Namely, the H/(H + D) ratio may be lower in the inner divertor than that in the outer divertor by the values of 0.15-0.35, depending on the conditions of gas puffing and plasma heating. This effect suggests the necessity of spatially-resolved measurements of isotope ratio in the divertor in the upcoming deuterium-tritium experiments. Also, separation of the overlapped T alpha and D alpha spectral lines is shown to be a challenging task especially when the local Doppler-broadened (Gaussian) line shapes are noticeably distorted by the net inward flux of fast non-Maxwellian neutral atoms. We use the respective, formerly developed model of an asymmetric spectral line shape, while analysing the data of the first deuterium-tritium experiment in JET-C (carbon wall), and test the model via comparing the isotope ratio results with another diagnostic's measurements. This model is shown to increase the accuracy of tritium concentration measurements in the divertor.
V.S. Neverov, A.B. Kukushkin, U. Kruezi, M.F. Stamp, H. Weisen, et al.. Determination of isotope ratio in the divertor of JET-ILW by high-resolution H α spectroscopy: H–D experiment and implications for D–T experiment. Nuclear Fusion, IOP Publishing, 2019, 59 (4), pp.046011. ⟨10.1088/1741-4326/ab0000⟩. ⟨hal-02177120⟩
P. Ström, P. Petersson, M. Rubel, E. Fortuna-Zaleśna, A. Widdowson, et al.. Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall. Journal of Nuclear Materials, Elsevier, 2019, 516, pp.202-213. ⟨10.1016/j.jnucmat.2018.11.027⟩. ⟨hal-02177126⟩ Plus de détails...
Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analysed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 mu m were indicated, but typical values were on the order of a few hundred nm. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 mu m were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.
P. Ström, P. Petersson, M. Rubel, E. Fortuna-Zaleśna, A. Widdowson, et al.. Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall. Journal of Nuclear Materials, Elsevier, 2019, 516, pp.202-213. ⟨10.1016/j.jnucmat.2018.11.027⟩. ⟨hal-02177126⟩
Davide Galassi, Guido Ciraolo, Patrick Tamain, Hugo Bufferand, Philippe Ghendrih, et al.. Tokamak Edge Plasma Turbulence Interaction with Magnetic X-Point in 3D Global Simulations. Fluids, MDPI, 2019, 4 (1), pp.50. ⟨10.3390/fluids4010050⟩. ⟨hal-02176982⟩ Plus de détails...
Turbulence in the edge plasma of a tokamak is a key actor in the determination of the confinement properties. The divertor configuration seems to be beneficial for confinement, suggesting an effect on turbulence of the particular magnetic geometry introduced by the X-point. Simulations with the 3D fluid turbulence code TOKAM3X are performed here to evaluate the impact of a diverted configuration on turbulence in the edge plasma, in an isothermal framework. The presence of the X-point is found, locally, to affect both the shape of turbulent structures and the amplitude of fluctuations, in qualitative agreement with recent experimental observations. In particular, a quiescent region is found in the divertor scrape-off layer (SOL), close to the separatrix. Globally, a mild transport barrier spontaneously forms in the closed flux surfaces region near the separatrix, differently from simulations in limiter configuration. The effect of turbulence-driven Reynolds stress on the formation of the barrier is found to be weak by dedicated simulations, while turbulence damping around the X-point seems to globally reduce turbulent transport on the whole flux surface. The magnetic shear is thus pointed out as a possible element that contributes to the formation of edge transport barriers.
Davide Galassi, Guido Ciraolo, Patrick Tamain, Hugo Bufferand, Philippe Ghendrih, et al.. Tokamak Edge Plasma Turbulence Interaction with Magnetic X-Point in 3D Global Simulations. Fluids, MDPI, 2019, 4 (1), pp.50. ⟨10.3390/fluids4010050⟩. ⟨hal-02176982⟩
Marco Martins Afonso, Philippe Meliga, Eric Serre. Optimal Transient Growth in an Incompressible Flow past a Backward-Slanted Step. Fluids, MDPI, 2019, 4 (1), pp.33. ⟨10.3390/fluids4010033⟩. ⟨hal-02176963⟩ Plus de détails...
With the aim of providing a first step in the quest for a reduction of the aerodynamic drag on the rear-end of a car, we study the phenomena of separation and reattachment of an incompressible flow by focusing on a specific aerodynamic geometry, namely a backward-slanted step at 25 circle of inclination. The ensuing recirculation bubble provides the basis for an analytical and numerical investigation of streamwise-streak generation, lift-up effect, and turbulent-wake and Kelvin-Helmholtz instabilities. A linear stability analysis is performed, and an optimal control problem with a steady volumic forcing is tackled by means of a variational formulation, adjoint methods, penalization schemes, and an orthogonalization algorithm. Dealing with the transient growth of spanwise-periodic perturbations, and inspired by the need of physically-realizable disturbances, we finally provide a procedure attaining a kinetic-energy maximal gain on the order of 106, with respect to the power introduced by the external forcing.
Marco Martins Afonso, Philippe Meliga, Eric Serre. Optimal Transient Growth in an Incompressible Flow past a Backward-Slanted Step. Fluids, MDPI, 2019, 4 (1), pp.33. ⟨10.3390/fluids4010033⟩. ⟨hal-02176963⟩
Gauthier Wissocq, Pierre Sagaut, Jean-François Boussuge. An extended spectral analysis of the lattice Boltzmann method: modal interactions and stability issues. Journal of Computational Physics, Elsevier, 2019, 380, pp.311-333. ⟨10.1016/j.jcp.2018.12.015⟩. ⟨hal-02176969⟩ Plus de détails...
An extension of the von Neumann linear analysis is proposed for the study of the discrete-velocity Boltzmann equation (DVBE) and the lattice Boltzmann (LB) scheme. While the standard technique is restricted to the investigation of the spectral radius and the dissipation and dispersion properties, a new focus is put here on the information carried by the modes. The technique consists in the computation of the moments of the eigenvectors and their projection onto the physical waves expected by the continuous linearized Navier-Stokes (NS) equations. The method is illustrated thanks to some simulations with the BGK (Bhatnagar-Gross-Krook) collision operator on the D2Q9 and D2V17 lattices. The present analysis reveals the existence of two kinds of modes: non-observable modes that do not carry any macroscopic information and observable modes. The latter may carry either a physical wave expected by the NS equations, or an unphysical information. Further investigation of modal interactions highlights a phenomenon called curve veering occurring between two observable modes: a swap of eigenvectors and dissipation rate is observed between the eigencurves. Increasing the Mach number of the mean flow yields an eigenvalue collision at the origin of numerical instabilities of the BGK model, arising from the error in the time and space discretization of the DVBE. (C) 2019 Elsevier Inc. All rights reserved.
Gauthier Wissocq, Pierre Sagaut, Jean-François Boussuge. An extended spectral analysis of the lattice Boltzmann method: modal interactions and stability issues. Journal of Computational Physics, Elsevier, 2019, 380, pp.311-333. ⟨10.1016/j.jcp.2018.12.015⟩. ⟨hal-02176969⟩
K. Lawson, K Aggarwal, I. Coffey, K Keenan, M O’mullane, et al.. Population modelling of the He II energy levels in tokamak plasmas: I. Collisional excitation model. Journal of Physics B: Atomic, Molecular and Optical Physics, IOP Publishing, 2019, 52 (4), pp.045001. ⟨10.1088/1361-6455/aaf703⟩. ⟨hal-02177115⟩ Plus de détails...
Helium is widely used as a fuel or minority gas in laboratory fusion experiments, and will be present as ash in DT thermonuclear plasmas. It is therefore essential to have a good understanding of its atomic physics. To this end He II population modelling has been undertaken for the spectroscopic levels arising from shells with principal quantum number n = 1-5. This paper focuses on a collisional excitation model; ionisation and recombination will be considered in a subsequent article. Heavy particle collisional excitation rate coefficients have been generated to supplement the currently-available atomic data for He II, and are presented for proton, deuteron, triton and alpha-particle projectiles. The widely-used criterion for levels within an n shell being populated in proportion to their statistical weights is reassessed with the most recent atomic data, and found not to apply to the He II levels at tokamak densities (10(18)-10(21) m(-3)). Consequences of this and other likely sources of errors are quantified, as is the effect of differing electron and ion temperatures. Line intensity ratios, including the so-called 'branching ratios' and the fine-structure beta(1), beta(2), beta(3), and gamma ratios, are discussed, the latter with regard to their possible use as diagnostics.
K. Lawson, K Aggarwal, I. Coffey, K Keenan, M O’mullane, et al.. Population modelling of the He II energy levels in tokamak plasmas: I. Collisional excitation model. Journal of Physics B: Atomic, Molecular and Optical Physics, IOP Publishing, 2019, 52 (4), pp.045001. ⟨10.1088/1361-6455/aaf703⟩. ⟨hal-02177115⟩
Journal: Journal of Physics B: Atomic, Molecular and Optical Physics
T. Vasilopoulou, I.E. Stamatelatos, P. Batistoni, A. Colangeli, D. Flammini, et al.. Improved neutron activation dosimetry for fusion. Fusion Engineering and Design, Elsevier, 2019, 139, pp.109-114. ⟨10.1016/j.fusengdes.2019.01.002⟩. ⟨hal-02177100⟩ Plus de détails...
Neutron activation technique has been widely used for the monitoring of neutron fluence at the Joint European Torus (JET) whereas it is foreseen to be employed at future fusion plants, such as ITER and DEMO. Neutron activation provides a robust tool for the measurement of neutron fluence in the complex environment encountered in a tokamak. However, activation experiments previously performed at JET showed that the activation foils used need to be calibrated in a real fusion environment in order to provide accurate neutron fluence data. Triggered by this challenge, an improved neutron activation method for the evaluation of neutron fluence at fusion devices has been developed. Activation assemblies similar to those used at JET were irradiated under 14 MeV neutrons at the Frascati Neutron Generator (FNG) reference neutron field. The data obtained from the calibration experiment were applied for the analysis of activation foil measurements performed during the implemented JET Deuterium-Deuterium (D-D) campaign. The activation results were compared against thermoluminescence measurements and a satisfactory agreement was observed. The proposed method provides confidence on the use of activation technique for the precise estimation of neutron fluence at fusion devices and enables its successful implementation in the forthcoming JET Deuterium-Tritium (D-T) campaign.
T. Vasilopoulou, I.E. Stamatelatos, P. Batistoni, A. Colangeli, D. Flammini, et al.. Improved neutron activation dosimetry for fusion. Fusion Engineering and Design, Elsevier, 2019, 139, pp.109-114. ⟨10.1016/j.fusengdes.2019.01.002⟩. ⟨hal-02177100⟩
A. Drenik, S. Brezinsek, P. Carvalho, V. Huber, N. Osterman, et al.. Analysis of the outer divertor hot spot activity in the protection video camera recordings at JET. Fusion Engineering and Design, Elsevier, 2019, 139, pp.115-123. ⟨10.1016/j.fusengdes.2018.12.079⟩. ⟨hal-02177109⟩ Plus de détails...
Hot spots on the divertor tiles at JET result in overestimation of the tile surface temperature which causes unnecessary termination of pulses. However, the appearance of hot spots can also indicate the condition of the divertor tile surfaces. To analyse the behaviour of the hot spots in the outer divertor tiles of JET, a simple image processing algorithm is developed. The algorithm isolates areas of bright pixels in the camera image and compares them to previously identified hot spots. The activity of the hot spots is then linked to values of other signals and parameters in the same time intervals. The operation of the detection algorithm was studied in a limited pulse range with high hot spot activity on the divertor tiles 5, 6 and 7. This allowed us to optimise the values of the controlling parameters. Then, the wider applicability of the method has been demonstrated by the analysis of the hot spot behaviour in a whole experimental campaign.
A. Drenik, S. Brezinsek, P. Carvalho, V. Huber, N. Osterman, et al.. Analysis of the outer divertor hot spot activity in the protection video camera recordings at JET. Fusion Engineering and Design, Elsevier, 2019, 139, pp.115-123. ⟨10.1016/j.fusengdes.2018.12.079⟩. ⟨hal-02177109⟩
F. Muller, A. Burbeau, B.-J. Gréa, Pierre Sagaut. Minimum enstrophy principle for two-dimensional inviscid flows around obstacles. Physical Review E , American Physical Society (APS), 2019, 99 (2), ⟨10.1103/PhysRevE.99.023105⟩. ⟨hal-02176949⟩ Plus de détails...
Large-scale coherent structures emerging in two-dimensional flows can be predicted from statistical physics inspired methods consisting in minimizing the global enstrophy while conserving the total energy and circulation in the Euler equations. In many situations, solid obstacles inside the domain may also constrain the flow and have to be accounted for via a minimum enstrophy principle. In this work, we detail this extended variational formulation and its numerical resolution. It is shown from applications to complex geometries containing multiple circular obstacles that the number of solutions is enhanced, allowing many possibilities of bifurcations for the large-scale structures. These phase change phenomena can explain the downstream recombinations of the flow in rod-bundle experiments and simulations.
F. Muller, A. Burbeau, B.-J. Gréa, Pierre Sagaut. Minimum enstrophy principle for two-dimensional inviscid flows around obstacles. Physical Review E , American Physical Society (APS), 2019, 99 (2), ⟨10.1103/PhysRevE.99.023105⟩. ⟨hal-02176949⟩
Lucie Merlier, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann large-eddy simulation of pollutant dispersion in complex urban environment with dense gas effect: Model evaluation and flow analysis. Building and Environment, Elsevier, 2019, 148, pp.634-652. ⟨hal-01995325⟩ Plus de détails...
Lucie Merlier, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann large-eddy simulation of pollutant dispersion in complex urban environment with dense gas effect: Model evaluation and flow analysis. Building and Environment, Elsevier, 2019, 148, pp.634-652. ⟨hal-01995325⟩
D.M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Effect of turbulent fluctuations on neutral particles transport with the TOKAM3X-EIRENE turbulence code. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.105-110. ⟨10.1016/j.nme.2018.12.011⟩. ⟨hal-02176529⟩ Plus de détails...
The effect of turbulent fluctuations on the transport of neutral particles (atoms, molecules) in tokamak plasmas is investigated with the 3D global turbulence code TOKAM3X-EIRENE in limiter geometry. The statistical properties of turbulent fields relevant to this work are discussed, including the recycling flux. The neutral particle transport is recalculated on the mean field plasma, and compared to the mean neutral particle density/flows obtained from the turbulent simulation, so as to assess the effects of the fluctuations, in particular on the ionization balance. The latter effects are remarkably modest in the simulation presented here, but are expected to become more and more pronounced as the high recycling regime is approached, in particular because the plasma temperature becomes low enough so that ionization is strongly non-linear. However, the turbulent fluctuations in the SOL do have a substantial effect on the neutral densities on the low field side of the limiter, including in the confined plasma. These effects are traced back to non-linearities in the plasma flux at the wall, and the fluctuations in the latter are identified as an important contributor both to neutral particle density fluctuations and to deviations from mean neutral particle density/flows in the turbulent simulation with respect to the same quantities recalculated on the mean plasma fields.
D.M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Effect of turbulent fluctuations on neutral particles transport with the TOKAM3X-EIRENE turbulence code. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.105-110. ⟨10.1016/j.nme.2018.12.011⟩. ⟨hal-02176529⟩
Simon Gsell, Rémi Bourguet, Marianna Braza. One- versus two-degree-of-freedom vortex-induced vibrations of a circular cylinder at Re=3900. Journal of Fluids and Structures, Elsevier, 2019, 85, pp.165-180. ⟨10.1016/j.jfluidstructs.2019.01.006⟩. ⟨hal-02062155⟩ Plus de détails...
The one- versus two-degree-of-freedom vortex-induced vibrations of a circular cylinder are investigated on the basis of direct numerical simulation results. The Reynolds number, based on the oncoming flow velocity and cylinder diameter, is set to 3900. Three cases are examined: the elastically mounted body is free to oscillate either in the direction aligned with the current (in-line direction; IL case), in the direction normal to the current (cross-flow direction; CF case), or in both directions (IL+CF case). In each case, the behavior of the flow–structure system is studied over a range of values of the reduced velocity (inverse of the oscillator natural frequency). The in-line and cross-flow responses observed in the IL+CF case substantially differ from their one-degree-of-freedom counterparts, especially in the intermediate reduced velocity region. In this region, no vibrations develop in the IL case and in-line oscillations only occur if cross-flow motion is allowed. These in-line oscillations are accompanied by a major increase of the cross-flow responses, compared to the CF case. The two-degree-of-freedom vibrations are associated with the emergence of large-amplitude higher harmonics in the fluid force spectra. These aspects and more specifically the impact of the existence of a degree-of-freedom and oscillations in a given direction, on the fluid force and structural response in the perpendicular direction, do not seem to be systematically connected to changes in wake topology. Here, they are discussed in light of the orientation and magnitude of the instantaneous flow velocity seen by the moving body.
Simon Gsell, Rémi Bourguet, Marianna Braza. One- versus two-degree-of-freedom vortex-induced vibrations of a circular cylinder at Re=3900. Journal of Fluids and Structures, Elsevier, 2019, 85, pp.165-180. ⟨10.1016/j.jfluidstructs.2019.01.006⟩. ⟨hal-02062155⟩
G. Sias, B. Cannas, A. Fanni, A. Murari, A. Pau, et al.. A locked mode indicator for disruption prediction on JET and ASDEX upgrade. Fusion Engineering and Design, Elsevier, 2019, 138, pp.254-266. ⟨10.1016/j.fusengdes.2018.11.021⟩. ⟨hal-02177084⟩ Plus de détails...
The aim of this paper is to present a signal processing algorithm that, applied to the raw Locked Mode signal, allows us to obtain a disruption indicator in principle exploitable on different tokamaks. A common definition of such an indicator for different machines would facilitate the development of portable systems for disruption prediction, which is becoming of increasingly importance for the next tokamak generations. Moreover, the indicator allows us to overcome some intrinsic problems in the diagnostic system such as drift and offset. The behavior of the proposed indicator as disruption predictor, based on crossing optimized thresholds of the signal amplitude, has been analyzed using data of both JET and ASDEX Upgrade experiments. A thorough analysis of the disruption prediction performance shows how the indicator is able to recover some missed and tardy detections of the raw signal. Moreover, it intervenes and corrects premature or even wrong alarms due to, e.g., drifts and/or offsets.
G. Sias, B. Cannas, A. Fanni, A. Murari, A. Pau, et al.. A locked mode indicator for disruption prediction on JET and ASDEX upgrade. Fusion Engineering and Design, Elsevier, 2019, 138, pp.254-266. ⟨10.1016/j.fusengdes.2018.11.021⟩. ⟨hal-02177084⟩
Philippe Meliga, E. Hachem. Time-accurate calculation and bifurcation analysis of the incompressible flow over a square cavity using variational multiscale modeling. Journal of Computational Physics, Elsevier, 2019, 376, pp.952-972. ⟨hal-01946893⟩ Plus de détails...
A thorough variational multiscale (VMS) modeling of the Navier-Stokes equations is used to compute numerical solutions of the incompressible flow over an open cavity. This case features several competing instabilities, and is highly challenging for VMS methods with regard to frequency and pattern selection, because of the non-normality of the linearized Navier-Stokes operator. The relevance of the approach is thus carefully assessed by comparing to direct numerical simulation (DNS) data benchmarked at several Reynolds numbers, and highly accurate time advancing methods are shown to predict relevant evolutions of the transient and saturated solutions. The VMS reduces substantially the computational cost, by similar to 35% (resp. similar to 60%) in terms of CPU time using a semi-implicit discretization scheme based on backward differentiation formula (resp. the implicit Crank-Nicholson scheme), and by similar to 80% in terms of memory requirement. Eventually, the highly efficient semi-implicit VMS numerical framework is used to unravel the onset of the flow oscillations and the selection of the limit cycle frequency, that happens to involve a subcritical Neimark-Sacker bifurcation.
Philippe Meliga, E. Hachem. Time-accurate calculation and bifurcation analysis of the incompressible flow over a square cavity using variational multiscale modeling. Journal of Computational Physics, Elsevier, 2019, 376, pp.952-972. ⟨hal-01946893⟩
Y. Hatano, S.E. Lee, J. Likonen, S. Koivuranta, M. Hara, et al.. Tritium distributions on W-coated divertor tiles used in the third JET ITER-like wall campaign. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.258-261. ⟨10.1016/j.nme.2019.01.001⟩. ⟨hal-02177095⟩ Plus de détails...
Tritium (T) distributions on tungsten (W)-coated plasma-facing tiles used in the third ITER-like wall campaign (2015-2016) of the Joint European Torus (JET) were examined by means of an imaging plate technique and beta-ray induced x-ray spectrometry, and they were compared with the distributions after the second (2013-2014) campaign. Strong enrichment of T in beryllium (Be) deposition layers was observed after the second campaign. In contrast, T distributions after the third campaign was more uniform though Be deposition layers were visually recognized. The one of the possible explanations is enhanced desorption of T from Be deposition layers due to higher tile temperatures caused by higher energy input in the third campaign.
Y. Hatano, S.E. Lee, J. Likonen, S. Koivuranta, M. Hara, et al.. Tritium distributions on W-coated divertor tiles used in the third JET ITER-like wall campaign. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.258-261. ⟨10.1016/j.nme.2019.01.001⟩. ⟨hal-02177095⟩
H. Bufferand, P. Tamain, S. Baschetti, J. Bucalossi, G. Ciraolo, et al.. Three-dimensional modelling of edge multi-component plasma taking into account realistic wall geometry. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.82-86. ⟨10.1016/j.nme.2018.11.025⟩. ⟨hal-02176521⟩ Plus de détails...
H. Bufferand, P. Tamain, S. Baschetti, J. Bucalossi, G. Ciraolo, et al.. Three-dimensional modelling of edge multi-component plasma taking into account realistic wall geometry. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.82-86. ⟨10.1016/j.nme.2018.11.025⟩. ⟨hal-02176521⟩
Lucie Merlier, Jérome Jacob, Pierre Sagaut. Lattice-Boltzmann large-eddy simulation of pollutant dispersion in complex urban environment with dense gas effect: Model evaluation and flow analysis. Building and Environment, Elsevier, 2019, 148, pp.634-652. ⟨10.1016/j.buildenv.2018.11.009⟩. ⟨hal-02176936⟩ Plus de détails...
The goal of this study is to assess the performance of an innovative Lattice Boltzmann (LB) - Large Eddy Simulation (LES) approach in simulating neutral and stratified pollutant dispersion in complex urban environments. Different simulations are performed for the central area of Paris, accounting for continuous neutral or non-neutral gas releases from a circular source located in both channeled or confined flows. Predicted concentrations are compared with detailed wind tunnel measurements from the MODITIC project (FFI, 2016). Results exhibit a good qualitative and quantitative agreement between numerical and experimental data for the different configurations studied. All the estimated quality metrics match acceptance criteria. In addition, it is shown that the new LBM LES approach is able to capture and highlight the key turbulent mechanisms underlying dispersion process in and above urban areas. Hence, being based on extensive and detailed simulations and quality assurance studies, this paper highlights that the developed approach is well suited to address urban dispersion issues, including accidental chemical releases and short term exposure problems. Such results are particularly valuable to support the design and use of fast response dispersion models.
Lucie Merlier, Jérome Jacob, Pierre Sagaut. Lattice-Boltzmann large-eddy simulation of pollutant dispersion in complex urban environment with dense gas effect: Model evaluation and flow analysis. Building and Environment, Elsevier, 2019, 148, pp.634-652. ⟨10.1016/j.buildenv.2018.11.009⟩. ⟨hal-02176936⟩
F. Nespoli, H. Bufferand, M. Valentinuzzi, N. Fedorczak, G. Ciraolo, et al.. Application of a two-fluid two-point model to SolEdge2D-EIRENE simulations of TCV H-mode plasma. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.29-34. ⟨10.1016/j.nme.2018.11.026⟩. ⟨hal-02176505⟩ Plus de détails...
The edge and scrape-off layer (SOL) plasma of the inter-ELM phase of an H-mode discharge from the TCV tokamak is modeled with the transport code SolEdge2D-EIRENE (Bufferand et al. Nuclear Fusion 55 (2015)). The numerical simulations, in presence and in absence of C impurities sputtered from the first wall, are presented and compared with the experiments, finding an overall good agreement. The application of the standard two-point model to the simulation results leads to an apparent momentum gain along the divertor leg. A two-fluid two-point model featuring thermally decoupled ions and electrons is introduced and applied to the simulation results, overcoming this apparent discrepancy.
F. Nespoli, H. Bufferand, M. Valentinuzzi, N. Fedorczak, G. Ciraolo, et al.. Application of a two-fluid two-point model to SolEdge2D-EIRENE simulations of TCV H-mode plasma. Nuclear Materials and Energy, Elsevier, 2019, 18, pp.29-34. ⟨10.1016/j.nme.2018.11.026⟩. ⟨hal-02176505⟩
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized thermal lattice Boltzmann model for high subsonic compressible flows. Journal of Computational Physics, Elsevier, 2019, 394, pp.82-99. ⟨hal-02142837⟩ Plus de détails...
A thermal lattice Boltzmann model with a hybrid recursive regularization (HRR) collision operator is developed on standard lattices for simulation of subsonic and sonic compressible flows without shock. The approach is hybrid: mass and momentum conservation equations are solved using a lattice Boltzmann solver, while the energy conservation is solved under entropy form with a finite volume solver. The defect of Galilean invariance related to Mach number is corrected by the third order equilibrium distribution function , supplemented by an additional correcting term and hybrid recursive regularization. The proposed approach is assessed considering the simulation of i) an isentropic vortex convection, ii) a two dimensional acoustic pulse and iii) non-isothermal Gaussian pulse with Ma number in range of 0 to 1. Numerical simulations demonstrate that the flaw in Galilean invari-ance is effectively eliminated by the compressible HRR model. At last, the compressible laminar flows over flat plate at Ma number of 0.3 and 0.87, Reynolds number of 10 5 are considered to validate the capture of viscous and diffusive effects.
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized thermal lattice Boltzmann model for high subsonic compressible flows. Journal of Computational Physics, Elsevier, 2019, 394, pp.82-99. ⟨hal-02142837⟩
Marcello Meldi, L. Djenidi, R. Antonia. Reynolds number effect on the velocity derivative flatness factor. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 856, pp.426-443. ⟨hal-01947035⟩ Plus de détails...
This paper investigates the effect of a finite Reynolds number (FRN) on the flatness factor (F) of the velocity derivative in decaying homogeneous isotropic turbulence by applying the eddy damped quasi-normal Markovian (EDQNM) method to calculate all terms in an analytic expression for F (Djenidi et al., Phys. Fluids, vol. 29 (5), 2017b, 051702). These terms and hence F become constant when the Taylor microscale Reynolds number, Re A exceeds approximately 10(4). For smaller values of Re-lambda, F, like the skewness -S, increases with ReA; this behaviour is in quantitative agreement with experimental and direct numerical simulation data. These results indicate that one must first ensure that Re-lambda A is large enough for the FRN effect to he negligibly small before the hypotheses of Kolmogorov (Dokl. Akad. Nauk SSSR, vol. 30, 1941a, pp. 301-305; Dokl. Akad. Nauk SSSR, vol. 32, 1941b, pp. 16-18; J. Fluid Mech. vol. 13, 1962, pp. 82-85) can he assessed unambiguously. An obvious implication is that results from experiments and direct numerical simulations for which Re-lambda is well below 10(4) may not he immune from the FRN effect. Another implication is that a power-law increase of with respect to Re-lambda, as suggested by the Kolmogorov 1962 theory, is not tenable when Re-lambda is large enough.
Marcello Meldi, L. Djenidi, R. Antonia. Reynolds number effect on the velocity derivative flatness factor. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 856, pp.426-443. ⟨hal-01947035⟩
Giorgio Giorgiani, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, Elsevier, 2018, 374, pp.515-532. ⟨10.1016/j.jcp.2018.07.028⟩. ⟨hal-02114246⟩ Plus de détails...
Progressing toward more accurate and more efficient numerical codes forthe simulation of transport and turbulence in the edge plasma of tokamaks,we propose in this work a new hybrid discontinous Galerkin solver. Basedon 2D advection-diffusion conservation equations for the ion density and theparticle flux in the direction parallel to the magnetic field, the code simulatesplasma transport in the poloidal section of tokamaks, including the open fieldlines of the Scrape-off Layer (SOL) and the closed field lines of the core re-gion. The spatial discretization is based on a high-order hybrid DG schemeon unstructured meshes, which provides an arbitrary high-order accuracywhile reducing considerably the number of coupled degrees of freedom witha local condensation process. A discontinuity sensor is employed to identifycritical elements and regularize the solution with the introduction of artificialdiffusion. Based on a finite-element discretization, not constrained by a flux-aligned mesh, the code is able to describe plasma facing components of anycomplex shape using Bohm boundary conditions and to simulate the plasmain versatile magnetic equilibria, possibly extended up to the center. Nu-merical tests using a manufacturated solution show appropriate convergenceorders when varying independently the number of elements or the degree ofinterpolation. Validation is performed by benchmarking the code with thewell-referenced edge transport code SOLEDGE2D (Bufferandet al.2013,2015 [1, 2]) in the WEST geometry. Final numerical experiments show thecapacity of the code to deal with low-diffusion solutions.
Giorgio Giorgiani, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, Elsevier, 2018, 374, pp.515-532. ⟨10.1016/j.jcp.2018.07.028⟩. ⟨hal-02114246⟩
Giorgio Giorgiani, H. Bufferand, G. Ciraolo, P. Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, Elsevier, 2018, 374, pp.515-532. ⟨10.1016/j.jcp.2018.07.028⟩. ⟨hal-01946999⟩ Plus de détails...
Progressing toward more accurate and more efficient numerical codes for the simulation of transport and turbulence in the edge plasma of tokamaks, we propose in this work a new hybrid discontinuous Galerkin solver. Based on 2D advection-diffusion conservation equations for the ion density and the particle flux in the direction parallel to the magnetic field, the code simulates plasma transport in the poloidal section of tokamaks, including the open field lines of the Scrape-off Layer (SOL) and the closed field lines of the core region. The spatial discretization is based on a high-order hybrid DG scheme on unstructured meshes, which provides an arbitrary high-order accuracy while reducing considerably the number of coupled degrees of freedom with a local condensation process. A discontinuity sensor is employed to identify critical elements and regularize the solution with the introduction of artificial diffusion. Based on a finite-element discretization, not constrained by a flux-aligned mesh, the code is able to describe plasma facing components of any complex shape using Bohm boundary conditions and to simulate the plasma in versatile magnetic equilibria, possibly extended up to the center. Numerical tests using a manufactured solution show appropriate convergence orders when varying independently the number of elements or the degree of interpolation. Validation is performed by benchmarking the code with the well-referenced edge transport code SOLEDGE2D (Bufferand et al., 2013, 2015 [1,2]) in the WEST geometry. Final numerical experiments show the capacity of the code to deal with low-diffusion solutions.
Giorgio Giorgiani, H. Bufferand, G. Ciraolo, P. Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, Elsevier, 2018, 374, pp.515-532. ⟨10.1016/j.jcp.2018.07.028⟩. ⟨hal-01946999⟩
Lucie Merlier, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann Large-Eddy Simulation of pollutant dispersion in street canyons including tree planting effects. Atmospheric Environment, Elsevier, 2018, 195, pp.89-103. ⟨10.1016/j.atmosenv.2018.09.040⟩. ⟨hal-02114676⟩ Plus de détails...
This study assesses the performance of a large eddy simulation (LES) based on the lattice Boltzmann method (LBM) in predicting near field dispersion in street canyons with tree planting. Based on a benchmark test case benefiting from wind tunnel measurements (CODASC), this study qualitatively and quantitatively discusses the prediction of traffic-induced pollutant concentration with respect to several reference studies. It also analyses the physics of the flow and concentration fields. Although the problem might seem rather simple, the flow is highlighted to be strongly three dimensional and transient. These properties enhance pollutant dispersion in the empty street canyon but air flow velocity and turbulence intensity tend to decrease in tree crowns. This effect of trees increases both mean and peak concentration levels at pedestrian level, which may be problematic in cities with dense traffic. These results show that LBM-LES is particularly well suited to study dispersion problems towards the development of more breathable cities.
Lucie Merlier, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann Large-Eddy Simulation of pollutant dispersion in street canyons including tree planting effects. Atmospheric Environment, Elsevier, 2018, 195, pp.89-103. ⟨10.1016/j.atmosenv.2018.09.040⟩. ⟨hal-02114676⟩
Lucie Merlier, Jérome Jacob, Pierre Sagaut. Lattice-Boltzmann Large-Eddy Simulation of pollutant dispersion in street canyons including tree planting effects. Atmospheric Environment, Elsevier, 2018, 195, pp.89-103. ⟨hal-01946898⟩ Plus de détails...
This study assesses the performance of a large eddy simulation (LES) based on the lattice Boltzmann method (LBM) in predicting near field dispersion in street canyons with tree planting. Based on a benchmark test case benefiting from wind tunnel measurements (CODASC), this study qualitatively and quantitatively discusses the prediction of traffic-induced pollutant concentration with respect to several reference studies. It also analyses the physics of the flow and concentration fields. Although the problem might seem rather simple, the flow is highlighted to be strongly three dimensional and transient. These properties enhance pollutant dispersion in the empty street canyon but air flow velocity and turbulence intensity tend to decrease in tree crowns. This effect of trees increases both mean and peak concentration levels at pedestrian level, which may be problematic in cities with dense traffic. These results show that LBM-LES is particularly well suited to study dispersion problems towards the development of more breathable cities.
Lucie Merlier, Jérome Jacob, Pierre Sagaut. Lattice-Boltzmann Large-Eddy Simulation of pollutant dispersion in street canyons including tree planting effects. Atmospheric Environment, Elsevier, 2018, 195, pp.89-103. ⟨hal-01946898⟩
Jérôme Jacob, Orestis Malaspinas, Pierre Sagaut. A new hybrid recursive regularised Bhatnagar–Gross–Krook collision model for Lattice Boltzmann method-based large eddy simulation. Journal of Turbulence, Taylor & Francis, 2018, pp.1 - 26. ⟨10.1080/14685248.2018.1540879⟩. ⟨hal-02114308⟩ Plus de détails...
A new Lattice Boltzmann collision model for large eddy simulation (LES) of weakly compressible flows is proposed. This model, referred to as the Hybrid Recursive Regularised Bhatnagar-Gross-Krook (HRR-BGK) model, is based on a modification of previously existing regularised collision models defined with the BGK Lattice Boltzmann method (LBM) framework. By hybridising the computation of the velocity gradient with an adequate Finite Difference scheme when reconstructing the non-equilibrium parts of the distribution function , a hyperviscosity term is introduced in the momentum equation, whose amplitude can be explicitly tuned via a weighting parameter. A dynamic version of the HRR-BGK is also proposed, in which the control parameter is tuned at each grid point and each time step in order to recover an arbitrarily fixed total dissipation. This new collision model is assessed for both explicit and implicit LES considering the flow around a circular cylinder at Re = 3900. The dynamic HRR-BGK is observed to yield very accurate results when equipped with Vreman's subgrid model to compute the target dissipation.
Jérôme Jacob, Orestis Malaspinas, Pierre Sagaut. A new hybrid recursive regularised Bhatnagar–Gross–Krook collision model for Lattice Boltzmann method-based large eddy simulation. Journal of Turbulence, Taylor & Francis, 2018, pp.1 - 26. ⟨10.1080/14685248.2018.1540879⟩. ⟨hal-02114308⟩
Jérôme Jacob, Orestis Malaspinas, Pierre Sagaut. A new hybrid recursive regularised Bhatnagar–Gross–Krook collision model for Lattice Boltzmann method-based large eddy simulation. Journal of Turbulence, Taylor & Francis, 2018, pp.1 - 26. ⟨10.1080/14685248.2018.1540879⟩. ⟨hal-01937009⟩ Plus de détails...
Jérôme Jacob, Orestis Malaspinas, Pierre Sagaut. A new hybrid recursive regularised Bhatnagar–Gross–Krook collision model for Lattice Boltzmann method-based large eddy simulation. Journal of Turbulence, Taylor & Francis, 2018, pp.1 - 26. ⟨10.1080/14685248.2018.1540879⟩. ⟨hal-01937009⟩
Cédric Reux, Sébastien Kahn, L. Zani, Bernard Pégourié, N. Piot, et al.. DEMO design using the SYCOMORE system code: Influence of technological constraints on the reactor performances. Fusion Engineering and Design, Elsevier, 2018, 136, pp.1572-1576. ⟨10.1016/j.fusengdes.2018.05.059⟩. ⟨hal-02115524⟩ Plus de détails...
The next step for fusion energy after the ITER tokamak is the demonstration power plant DEMO. In this framework , system codes are used to address high-level key design issues for the DEMO pre-conceptual phase. They aim at capturing the interactions between the subsystems of a fusion reactor. SYCOMORE is a modular system code which includes physics and technology models coupled to an optimizer in order to explore a large design parameter space. In the present paper, trade-off studies focused on technology modules are reported including the influence of some design-driving assumptions on the reactor performances and size, starting from a European DEMO1-like design (more than 500 MW net electric power and 2 h burn duration). The increase of the mechanical stress limits in TF and CS magnets can help reducing the reactor size, slightly more when high temperature superconductors are used in the TF coil. The tritium breeding ratio can be improved to more than 1.10 by a moderate increase of the size, but the tritium burn-up ratio needs one additional meter of major radius for every percent increase. Divertor coolant options are also compared, showing some differences between helium, hot and cold water scenarios at various incident divertor heat fluxes.
Cédric Reux, Sébastien Kahn, L. Zani, Bernard Pégourié, N. Piot, et al.. DEMO design using the SYCOMORE system code: Influence of technological constraints on the reactor performances. Fusion Engineering and Design, Elsevier, 2018, 136, pp.1572-1576. ⟨10.1016/j.fusengdes.2018.05.059⟩. ⟨hal-02115524⟩
C. Reux, S. Kahn, L. Zani, B. Pégourié, N. Piot, et al.. DEMO design using the SYCOMORE system code: Influence of technological constraints on the reactor performances. Fusion Engineering and Design, Elsevier, 2018, 136, pp.1572-1576. ⟨hal-02015507⟩ Plus de détails...
The next step for fusion energy after the ITER tokamak is the demonstration power plant DEMO. In this framework, system codes are used to address high-level key design issues for the DEMO pre-conceptual phase. They aim at capturing the interactions between the subsystems of a fusion reactor. SYCOMORE is a modular system code which includes physics and technology models coupled to an optimizer in order to explore a large design parameter space. In the present paper, trade-off studies focused on technology modules are reported including the influence of some design-driving assumptions on the reactor performances and size, starting from a European DEMO1-like design (more than 500 MW net electric power and 2 h burn duration). The increase of the mechanical stress limits in TF and CS magnets can help reducing the reactor size, slightly more when high temperature superconductors are used in the TF coil. The tritium breeding ratio can be improved to more than 1.10 by a moderate increase of the size, but the tritium burn-up ratio needs one additional meter of major radius for every percent increase. Divertor coolant options are also compared, showing some differences between helium, hot and cold water scenarios at various incident divertor heat fluxes.
C. Reux, S. Kahn, L. Zani, B. Pégourié, N. Piot, et al.. DEMO design using the SYCOMORE system code: Influence of technological constraints on the reactor performances. Fusion Engineering and Design, Elsevier, 2018, 136, pp.1572-1576. ⟨hal-02015507⟩
Philippe Ghendrih, Y. Asahi, E. Caschera, G. Dif-Pradalier, P. Donnel, et al.. Generation and dynamics of SOL corrugated profiles. Journal of Physics: Conference Series, IOP Publishing, 2018, 1125, pp.012011. ⟨10.1088/1742-6596/1125/1/012011⟩. ⟨hal-02196677⟩ Plus de détails...
The staircase transport regime reported in kinetic simulations of plasma turbulent transport in magnetic confinement is recovered with a simple 2D fluid model allowing for reduced damping of the zonal flows. Some of the complex dynamics of the kinetic zonation regime are recovered but the pattern of the corrugation appears to be sinusoidal with a characteristic scale comparable to that of turbulence modes with largest spectral energy, in contrast to regimes observed in global and flux-driven kinetic simulations. Enhanced zonal flows govern both an overall reduction of the SOL width and a gradual steepening of the gradients with distance to the separatrix.
Philippe Ghendrih, Y. Asahi, E. Caschera, G. Dif-Pradalier, P. Donnel, et al.. Generation and dynamics of SOL corrugated profiles. Journal of Physics: Conference Series, IOP Publishing, 2018, 1125, pp.012011. ⟨10.1088/1742-6596/1125/1/012011⟩. ⟨hal-02196677⟩
Maria-Vittoria Salvetti, Marcelo Meldi, Luca Bruno, Pierre Sagaut. Reliability of Large-Eddy Simulations: Benchmarking and Uncertainty Quantification. Direct and Large-Eddy Simulation X, pp.15-23, 2018. ⟨hal-02115804⟩ Plus de détails...
Maria-Vittoria Salvetti, Marcelo Meldi, Luca Bruno, Pierre Sagaut. Reliability of Large-Eddy Simulations: Benchmarking and Uncertainty Quantification. Direct and Large-Eddy Simulation X, pp.15-23, 2018. ⟨hal-02115804⟩
M. Salvetti, Marcello Meldi, L. Bruno, Pierre Sagaut. Reliability of Large-Eddy Simulations: Benchmarking and Uncertainty Quantification. DIRECT AND LARGE-EDDY SIMULATION X (10th ERCOFTAC Workshop on Direct and Large Eddy Simulation (DLES)), 24, Springer, pp.15-23, 2018, ERCOFTAC Series. ⟨hal-01946977⟩ Plus de détails...
M. Salvetti, Marcello Meldi, L. Bruno, Pierre Sagaut. Reliability of Large-Eddy Simulations: Benchmarking and Uncertainty Quantification. DIRECT AND LARGE-EDDY SIMULATION X (10th ERCOFTAC Workshop on Direct and Large Eddy Simulation (DLES)), 24, Springer, pp.15-23, 2018, ERCOFTAC Series. ⟨hal-01946977⟩
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga, Eric Serre. A stabilized Powell–Sabin finite-element method for the 2D Euler equations in supersonic regime. Computer Methods in Applied Mechanics and Engineering, Elsevier, 2018, 340, pp.216-235. 〈hal-01947259〉 Plus de détails...
In this paper a Powell-Sabin finite-element (PS-REM) scheme is presented for the solution of the 2D Euler equations in supersonic regime. The spatial discretization is based on PS splines, that are piecewise quadratic polynomials with a global C-1 continuity, defined on conforming triangulations. Some geometrical issues related to the practical construction of the PS elements are discussed, in particular, the generation of the control triangles and the imposition of the boundary conditions. A stabilized formulation is considered, and a novel shock-capturing technique in the context of continuous finite-elements is proposed to reduce oscillations around the discontinuity, and compared with the classical technique proposed by Tezduyar and Senga (2006). The code is verified using manufactured solutions and validated using two challenging numerical examples, which allows to evaluate the performance of the PS discretization in capturing the shocks. (C) 2018 Elsevier B.V. All rights reserved.
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga, Eric Serre. A stabilized Powell–Sabin finite-element method for the 2D Euler equations in supersonic regime. Computer Methods in Applied Mechanics and Engineering, Elsevier, 2018, 340, pp.216-235. 〈hal-01947259〉
Journal: Computer Methods in Applied Mechanics and Engineering
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⟩
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (10), pp.105007. ⟨hal-01947253⟩ Plus de détails...
The impact of the del B-drift in the cross-field transport and its effect on the density and power scrape-off layer (SOL) width in the limit of low anomalous transport is studied with the fluid code SolEdge2D. In the first part of the work, the simulations are run with an isothermal reduced fluid model. It is found that a del B-drift dominated regime is reached in all geometries studied (JET-like, ASDEX-like and circular analytic geometries), and that the transition toward this regime comes along with the apparition of supersonic shocks, and a complex parallel equilibrium. The parametric dependencies of the SOL width in this regime are investigated, and the temperature and the poloidal magnetic field are found to be the principal parameters governing the evolution of the SOL width. In the second part of this paper, the impact of additional physics is studied (inclusion of the centrifugal drift, self-consistent variation of temperature and the treatment of the neutral species). The addition of centrifugal drift and neutral species are shown to play a role in the establishment of the parallel equilibrium, impacting the SOL's width, although the role of the centrifugal drift is limited to a low diffusion level. Finally, the numerical results are compared with the estimate of the Goldston's heuristic drift based model (HD-model), the starting point of our study, and which has shown good agreement with experimental scaling laws. We find that the particles SOL widths in the del B-drift dominated regime are at least two times smaller than the estimate of the HD-model. Moreover, in the parametric dependencies proposed by the HD-model, the dependency with B-pol is retrieved, but not the one on T.
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (10), pp.105007. ⟨hal-01947253⟩
Yong-Liang Feng, Shao-Long Guo, Wen-Quan Tao, Pierre Sagaut. Regularized thermal lattice Boltzmann method for natural convection with large temperature differences. International Journal of Heat and Mass Transfer, Elsevier, 2018, 125, pp.1379-1391. ⟨10.1016/j.ijheatmasstransfer.2018.05.051⟩. ⟨hal-02114047⟩ Plus de détails...
A new thermal lattice Boltzmann (LB) method is proposed for the simulation of natural convection with large temperature differences and high Rayleigh number. A regularization procedure is developed on LB equation with a third order expansion of equilibrium distribution functions, in which a temperature term is involved to recover the equation of state for perfect gas. A hybrid approach is presented to couple mass conservation equation, momentum conservation equations and temperature evolution equation. A simple and robust non-conservative form of temperature transport equation is adopted and solved by the finite volume method. A comparison study between classical Double Distribution Function (DDF) model and the hybrid finite volume model with different integration schemes is presented to demonstrate both consistency and accuracy of hybrid models. The proposed model is assessed by simulating several test cases, namely the two-dimensional non-Boussinesq natural convection in a square cavity with large horizontal temperature differences and two unsteady natural convection flows in a tall enclosure at high Rayleigh number. The present method can accurately predict both the steady and unsteady non-Boussinesq convection flows with significant heat transfer. For unsteady natural convection, oscillations with chaotic feature can be well captured in large temperature gradient conditions.
Yong-Liang Feng, Shao-Long Guo, Wen-Quan Tao, Pierre Sagaut. Regularized thermal lattice Boltzmann method for natural convection with large temperature differences. International Journal of Heat and Mass Transfer, Elsevier, 2018, 125, pp.1379-1391. ⟨10.1016/j.ijheatmasstransfer.2018.05.051⟩. ⟨hal-02114047⟩
Journal: International Journal of Heat and Mass Transfer
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (10), pp.105007. ⟨10.1088/1361-6587/aad650⟩. ⟨hal-02111781⟩ Plus de détails...
The impact of the del B-drift in the cross-field transport and its effect on the density and power scrape-off layer (SOL) width in the limit of low anomalous transport is studied with the fluid code SolEdge2D. In the first part of the work, the simulations are run with an isothermal reduced fluid model. It is found that a del B-drift dominated regime is reached in all geometries studied (JET-like, ASDEX-like and circular analytic geometries), and that the transition toward this regime comes along with the apparition of supersonic shocks, and a complex parallel equilibrium. The parametric dependencies of the SOL width in this regime are investigated, and the temperature and the poloidal magnetic field are found to be the principal parameters governing the evolution of the SOL width. In the second part of this paper, the impact of additional physics is studied (inclusion of the centrifugal drift, self-consistent variation of temperature and the treatment of the neutral species). The addition of centrifugal drift and neutral species are shown to play a role in the establishment of the parallel equilibrium, impacting the SOL's width, although the role of the centrifugal drift is limited to a low diffusion level. Finally, the numerical results are compared with the estimate of the Goldston's heuristic drift based model (HD-model), the starting point of our study, and which has shown good agreement with experimental scaling laws. We find that the particles SOL widths in the del B-drift dominated regime are at least two times smaller than the estimate of the HD-model. Moreover, in the parametric dependencies proposed by the HD-model, the dependency with B-pol is retrieved, but not the one on T.
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (10), pp.105007. ⟨10.1088/1361-6587/aad650⟩. ⟨hal-02111781⟩
Yong-Liang Feng, Shao-Long Guo, Wen-Quan Tao, Pierre Sagaut. Regularized thermal lattice Boltzmann method for natural convection with large temperature differences. International Journal of Heat and Mass Transfer, Elsevier, 2018, 125, pp.1379 - 1391. ⟨10.1016/j.ijheatmasstransfer.2018.05.051⟩. ⟨hal-01875603⟩ Plus de détails...
A new thermal lattice Boltzmann (LB) method is proposed for the simulation of natural convection with large temperature differences and high Rayleigh number. A regularization procedure is developed on LB equation with a third order expansion of equilibrium distribution functions, in which a temperature term is involved to recover the equation of state for perfect gas. A hybrid approach is presented to couple mass conservation equation, momentum conservation equations and temperature evolution equation. A simple and robust non-conservative form of temperature transport equation is adopted and solved by the finite volume method. A comparison study between classical Double Distribution Function (DDF) model and the hybrid finite volume model with different integration schemes is presented to demonstrate both consistency and accuracy of hybrid models. The proposed model is assessed by simulating several test cases, namely the two-dimensional non-Boussinesq natural convection in a square cavity with large horizontal temperature differences and two unsteady natural convection flows in a tall enclosure at high Rayleigh number. The present method can accurately predict both the steady and unsteady non-Boussinesq convection flows with significant heat transfer. For unsteady natural convection, oscillations with chaotic feature can be well captured in large temperature gradient conditions.
Yong-Liang Feng, Shao-Long Guo, Wen-Quan Tao, Pierre Sagaut. Regularized thermal lattice Boltzmann method for natural convection with large temperature differences. International Journal of Heat and Mass Transfer, Elsevier, 2018, 125, pp.1379 - 1391. ⟨10.1016/j.ijheatmasstransfer.2018.05.051⟩. ⟨hal-01875603⟩
Journal: International Journal of Heat and Mass Transfer
Romain Dupuis, Jean-Christophe Jouhaud, Pierre Sagaut. Surrogate Modeling of Aerodynamic Simulations for Multiple Operating Conditions Using Machine Learning. AIAA Journal, American Institute of Aeronautics and Astronautics, 2018, 56 (9), pp.3622 - 3635. ⟨10.2514/1.J056405⟩. ⟨hal-01875606⟩ Plus de détails...
This paper describes a methodology, called local decomposition method, which aims at building a surrogate model based on steady turbulent aerodynamic fields at multiple operating conditions. The various shapes taken by the aerodynamic fields due to the multiple operation conditions pose real challenges as well as the computational cost of the high-fidelity simulations. The developed strategy mitigates these issues by combining traditional surrogate models and machine learning. The central idea is to separate the solutions with a subsonic behavior from the transonic and high-gradient solutions. First, a shock sensor extracts a feature corresponding to the presence of discontinuities, easing the clustering of the simulations by an unsupervised learning algorithm. Second, a supervised learning algorithm divides the parameter space into subdomains, associated to different flow regimes. Local reduced-order models are built on each subdomain using proper orthogonal decomposition coupled with a multivariate interpolation tool. Finally, an improved resampling technique taking advantage of the subdomain decomposition minimizes the redundancy of sampling. The methodology is assessed on the turbulent two-dimensional flow around the RAE2822 transonic airfoil. It exhibits a significant improvement in terms of prediction accuracy for the developed strategy compared with the classical method of surrogate modeling.
Romain Dupuis, Jean-Christophe Jouhaud, Pierre Sagaut. Surrogate Modeling of Aerodynamic Simulations for Multiple Operating Conditions Using Machine Learning. AIAA Journal, American Institute of Aeronautics and Astronautics, 2018, 56 (9), pp.3622 - 3635. ⟨10.2514/1.J056405⟩. ⟨hal-01875606⟩
Romain Dupuis, Jean-Christophe Jouhaud, Pierre Sagaut. Surrogate Modeling of Aerodynamic Simulations for Multiple Operating Conditions Using Machine Learning. AIAA Journal, American Institute of Aeronautics and Astronautics, 2018, 56 (9), pp.3622-3635. ⟨10.2514/1.J056405⟩. ⟨hal-02113987⟩ Plus de détails...
This paper describes a methodology, called local decomposition method, which aims at building a surrogate model based on steady turbulent aerodynamic fields at multiple operating conditions. The various shapes taken by the aerodynamic fields due to the multiple operation conditions pose real challenges as well as the computational cost of the high-fidelity simulations. The developed strategy mitigates these issues by combining traditional surrogate models and machine learning. The central idea is to separate the solutions with a subsonic behavior from the transonic and high-gradient solutions. First, a shock sensor extracts a feature corresponding to the presence of discontinuities, easing the clustering of the simulations by an unsupervised learning algorithm. Second, a supervised learning algorithm divides the parameter space into subdomains, associated to different flow regimes. Local reduced-order models are built on each subdomain using proper orthogonal decomposition coupled with a multivariate interpolation tool. Finally, an improved resampling technique taking advantage of the subdomain decomposition minimizes the redundancy of sampling. The methodology is assessed on the turbulent two-dimensional flow around the RAE2822 transonic airfoil. It exhibits a significant improvement in terms of prediction accuracy for the developed strategy compared with the classical method of surrogate modeling.
Romain Dupuis, Jean-Christophe Jouhaud, Pierre Sagaut. Surrogate Modeling of Aerodynamic Simulations for Multiple Operating Conditions Using Machine Learning. AIAA Journal, American Institute of Aeronautics and Astronautics, 2018, 56 (9), pp.3622-3635. ⟨10.2514/1.J056405⟩. ⟨hal-02113987⟩
Marcello Meldi. Augmented Prediction of Turbulent Flows via Sequential Estimators Sensitivity of State Estimation to Density of Time Sampling for Available Observation. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2018, 101 (2), pp.389-412. ⟨10.1007/s10494-018-9967-6⟩. ⟨hal-02114575⟩ Plus de détails...
A sensitivity analysis of new methodological approaches for state estimation (Meldi and Poux J. Comput. Phys. 347, 207-234, 2017) is proposed in this manuscript. The performance of the estimator is tested via the analysis of a number of aspects that play a major role in the augmented prediction process, such as the density in time sampling of available observation, the placement of sensors and the interaction with boundary conditions. The work is developed for the turbulent spatially evolving mixing layer test case, using high precision DNS samples as observation and Smagorinsky LES as underlying model. A number of estimators combining LES with DNS data integrated via sensors are performed, varying the frequency of time sampling of observation f T = 1// T , where T is the period between successive assimilation phases. It is concluded that if T ≤≈ 0.5t A , where t A is the characteristic average advection time, the prediction via estimator shows minimal differences i.e. the process of state estimation has reached convergence. This relation can be interpreted as a threshold for converged state estimation. However, the results show as well that a linear converge towards pure model performance is not obtained for every physical quantity with progressive decrease of f T , while eventually pure model results are obtained for f T → 0. In addition, the effect of upstream boundary conditions over the state estimation are investigated and strategies for optimized positions of sensors are derived.
Marcello Meldi. Augmented Prediction of Turbulent Flows via Sequential Estimators Sensitivity of State Estimation to Density of Time Sampling for Available Observation. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2018, 101 (2), pp.389-412. ⟨10.1007/s10494-018-9967-6⟩. ⟨hal-02114575⟩
Marcello Meldi. Augmented Prediction of Turbulent Flows via Sequential Estimators. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2018, 101 (2), pp.389-412. ⟨hal-01947043⟩ Plus de détails...
A sensitivity analysis of new methodological approaches for state estimation (Meldi and Poux J. Comput. Phys. 347, 207-234, 2017) is proposed in this manuscript. The performance of the estimator is tested via the analysis of a number of aspects that play a major role in the augmented prediction process, such as the density in time sampling of available observation, the placement of sensors and the interaction with boundary conditions. The work is developed for the turbulent spatially evolving mixing layer test case, using high precision DNS samples as observation and Smagorinsky LES as underlying model. A number of estimators combining LES with DNS data integrated via sensors are performed, varying the frequency of time sampling of observation f (T) = 1/Delta (T) , where Delta (T) is the period between successive assimilation phases. It is concluded that if Delta (T) aeae 0.5t (A) , where t (A) is the characteristic average advection time, the prediction via estimator shows minimal differences i.e. the process of state estimation has reached convergence. This relation can be interpreted as a threshold for converged state estimation. However, the results show as well that a linear converge towards pure model performance is not obtained for every physical quantity with progressive decrease of f (T) , while eventually pure model results are obtained for f (T) -> 0. In addition, the effect of upstream boundary conditions over the state estimation are investigated and strategies for optimized positions of sensors are derived.
Marcello Meldi. Augmented Prediction of Turbulent Flows via Sequential Estimators. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2018, 101 (2), pp.389-412. ⟨hal-01947043⟩
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 849, pp.741 - 776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-02116002⟩ Plus de détails...
Variations in the local stability of the flow in a Taylor-Couette cell can be imposed by adding an axial Poiseuille flow and a radial flow associated with one or both of the cylinders being permeable. At a given rotation rate of the inner cylinder, this results in adjacent regions of the flow that can be simultaneously stable, convectively unstable, and absolutely unstable, making this system fit for studying global modes of instability. To this end, building on the existing stability analysis in absolute modes developing over axially invariant base flows, we consider the case of axially varying base flows in systems for which the outer cylinder is impermeable, and the inner cylinder is a weakly permeable membrane through which the radial flow is governed by Darcy's law. The frameworks of linear and nonlinear global modes are used to describe the instabilities and assess the results of direct numerical simulations using a dedicated pseudospectral method. Three different axially evolving set-ups are considered. In the first, fluid injection occurs along the full inner cylinder. In the second, fluid extraction occurs along the full inner cylinder. Besides its fundamental interest, this set-up is relevant to filtration devices. In the third, fluid flux through the inner cylinder evolves from extraction to injection as cross-flow reversal occurs. In agreement with the global mode analyses, the numerical simulations develop centrifugal instabilities above the predicted critical rotation rates and downstream of the predicted axial locations. The global mode analyses do not fully explain, however, that. the instabilities observed in the numerical simulations take the form of axial stacks of wavepackets characterized by jumps of the temporal frequency.
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 849, pp.741 - 776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-02116002⟩
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 849, pp.741-776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-01947280⟩ Plus de détails...
Variations in the local stability of the flow in a Taylor-Couette cell can be imposed by adding an axial Poiseuille flow and a radial flow associated with one or both of the cylinders being permeable. At a given rotation rate of the inner cylinder, this results in adjacent regions of the flow that can be simultaneously stable, convectively unstable, and absolutely unstable, making this system fit for studying global modes of instability. To this end, building on the existing stability analysis in absolute modes developing over axially invariant base flows, we consider the case of axially varying base flows in systems for which the outer cylinder is impermeable, and the inner cylinder is a weakly permeable membrane through which the radial flow is governed by Darcy's law. The frameworks of linear and nonlinear global modes are used to describe the instabilities and assess the results of direct numerical simulations using a dedicated pseudospectral method. Three different axially evolving set-ups are considered. In the first, fluid injection occurs along the full inner cylinder. In the second, fluid extraction occurs along the full inner cylinder. Besides its fundamental interest, this set-up is relevant to filtration devices. In the third, fluid flux through the inner cylinder evolves from extraction to injection as cross-flow reversal occurs. In agreement with the global mode analyses, the numerical simulations develop centrifugal instabilities above the predicted critical rotation rates and downstream of the predicted axial locations. The global mode analyses do not fully explain, however, that. the instabilities observed in the numerical simulations take the form of axial stacks of wavepackets characterized by jumps of the temporal frequency.
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 849, pp.741-776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-01947280⟩
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 849, pp.741 - 776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-01875615⟩ Plus de détails...
Variations in the local stability of the flow in a Taylor-Couette cell can be imposed by adding an axial Poiseuille flow and a radial flow associated with one or both of the cylinders being permeable. At a given rotation rate of the inner cylinder, this results in adjacent regions of the flow that can be simultaneously stable, convectively unstable, and absolutely unstable, making this system fit for studying global modes of instability. To this end, building on the existing stability analysis in absolute modes developing over axially invariant base flows, we consider the case of axially varying base flows in systems for which the outer cylinder is impermeable, and the inner cylinder is a weakly permeable membrane through which the radial flow is governed by Darcy's law. The frameworks of linear and nonlinear global modes are used to describe the instabilities and assess the results of direct numerical simulations using a dedicated pseudospectral method. Three different axially evolving set-ups are considered. In the first, fluid injection occurs along the full inner cylinder. In the second, fluid extraction occurs along the full inner cylinder. Besides its fundamental interest, this set-up is relevant to filtration devices. In the third, fluid flux through the inner cylinder evolves from extraction to injection as cross-flow reversal occurs. In agreement with the global mode analyses, the numerical simulations develop centrifugal instabilities above the predicted critical rotation rates and downstream of the predicted axial locations. The global mode analyses do not fully explain, however, that. the instabilities observed in the numerical simulations take the form of axial stacks of wavepackets characterized by jumps of the temporal frequency.
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 849, pp.741 - 776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-01875615⟩
Eunok Yim, J.-M. Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 848, pp.631 - 647. ⟨10.1017/jfm.2018.239⟩. ⟨hal-01875619⟩ Plus de détails...
The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor-stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Karman self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counter-clockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers m, in the range m is an element of [32, 78 ]. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.
Eunok Yim, J.-M. Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 848, pp.631 - 647. ⟨10.1017/jfm.2018.239⟩. ⟨hal-01875619⟩
Eunok Yim, J.-M. Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 848, pp.631 - 647. ⟨10.1017/jfm.2018.239⟩. ⟨hal-02116221⟩ Plus de détails...
The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor-stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Karman self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counter-clockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers m, in the range m is an element of [32, 78 ]. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.
Eunok Yim, J.-M. Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 848, pp.631 - 647. ⟨10.1017/jfm.2018.239⟩. ⟨hal-02116221⟩
Xiaoliang He, Sourabh Apte, Kai Schneider, Benjamin Kadoch. Angular multiscale statistics of turbulence in a porous bed. Physical Review Fluids, American Physical Society, 2018, 3 (8), ⟨10.1103/PhysRevFluids.3.084501⟩. ⟨hal-02081067⟩ Plus de détails...
Direct numerical simulation of pore-scale turbulence is performed in a unit cell of a face-centered cubic lattice at three different pore Reynolds numbers (300, 500, and 1000). The pore-geometry gives rise to very low porosity resulting in rapid acceleration and deceleration of the flow in different regions. Eulerian statistics of mean velocity and turbulent kinetic energy are first described to provide a good understanding of the overall flow topology. In addition, the spatial variances and probability density functions for the instantaneous and temporal fluctuation velocities are computed to assess the higher-order statistics. The flow field is then analyzed using angular Lagrangian multiscale statistics of fluid particles to study their directional change at different timescales. Two power laws are observed for the evolution of the mean absolute angle as a function of time lag, demarking the early time and an intermediate, inertial range. The effect of the geometric confinement on the asymptotic behavior of the angular statistics is examined in detail. An asymptotic limit different than π/2 (corresponding to equidistribution of the mean angle, observed for three-dimensional isotropic turbulence with periodic boundaries) or 2 3 π (observed for two-dimensional wall-bounded turbulence) is obtained, representing the strong effect of geometric confinement on turbulence. Besides, the probability density functions (PDFs) for the instantaneous curvature angles are computed and the normalized PDFs are fit to a Fisher distribution. Furthermore, a Monte Carlo-based stochastic model is developed to predict the asymptotic curvature angle.
Xiaoliang He, Sourabh Apte, Kai Schneider, Benjamin Kadoch. Angular multiscale statistics of turbulence in a porous bed. Physical Review Fluids, American Physical Society, 2018, 3 (8), ⟨10.1103/PhysRevFluids.3.084501⟩. ⟨hal-02081067⟩
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, pp.675-682. ⟨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, pp.675-682. ⟨10.1007/s12217-018-9645-2⟩. ⟨hal-01847206⟩
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, pp.675-682. ⟨10.1007/s12217-018-9645-2⟩. ⟨hal-02112826⟩ 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, pp.675-682. ⟨10.1007/s12217-018-9645-2⟩. ⟨hal-02112826⟩
H. Bufferand, G. Ciraolo, P. Di Cintio, N. Fedorczak, Ph. Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.563-569. ⟨hal-01947239⟩ Plus de détails...
The non-local expression proposed by Luciani-Mora-Virmont is implemented in a one dimensional fluid model for the scrape-off layer. Analytical solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The non-local heat flux is compared to the Spitzer-Harm heat flux for different collisionality.
H. Bufferand, G. Ciraolo, P. Di Cintio, N. Fedorczak, Ph. Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.563-569. ⟨hal-01947239⟩
L. Valade, A. Ekedahl, Philippe Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02196679⟩ Plus de détails...
Hot spot generation by Lower Hybrid (LH) launchers is found to be governed by a resonance in the plasma electric field response to the external drive. The kinetic analysis in 1D-1V in the parallel direction allows one to compute the amplification effect for small amplitude of the external drive. The resonant Lorentzian response distorts the distribution function with an island structure in the suprathermal part at the phase velocity of the external electrostatic drive. The non-linear features enhance the plasma response driving overlap effects between multiple waves at rather low amplitude. The onset of a plateau in the distribution function with extent up to one thermal velocity is already obtained when the standard overlap condition is achieved. The sensitivity of the resonance to plasma parameters and large variation of the amplification magnitude can compensate the fast radial decay of 1
L. Valade, A. Ekedahl, Philippe Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02196679⟩
L. Valade, A. Ekedahl, P. Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. ⟨hal-01947214⟩ Plus de détails...
Hotspot generation by lower-hybrid (LH) launchers is found to be governed by a resonance in the plasma electric field response to the external drive. The kinetic analysis in 1D-1V in the parallel direction allows one to compute the amplification effect for small amplitude of the external drive. The resonant Lorentzian response distorts the distribution function. An island structure is formed in the suprathermal part at the phase velocity of the external electrostatic drive. The non-linear features enhance the plasma response, driving overlap effects between multiple waves at rather low amplitude. The onset of a plateau in the distribution function, with extent reaching one thermal velocity, is already obtained when the standard overlap condition is achieved. The sensitivity of the resonance to plasma parameters and large variation of the amplification magnitude can compensate the fast radial decay of the small-scale features generated by the LH launchers, which are responsible for the interaction with the cold electrons. This mechanism can trigger hotspot generation further in the scrape-off layer than otherwise expected.
L. Valade, A. Ekedahl, P. Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. ⟨hal-01947214⟩
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.457-464. ⟨hal-01947205⟩ Plus de détails...
In order to improve the presently used ad hoc flux limiter treatment of parallel heat flux transport in edge plasma fluid codes, here, we consider a generalized version of the Fourier law implementing a non-local kernel for the heat flux computation. The Bohm boundary condition at the wall is recovered, introducing a volumetric loss term representing the contribution of suprathermal particles to the energy out flux. As expected, this contribution is negligible in the strongly collisional regime, while it becomes more and more dominant for marginally and low-collisional regimes. In the second part of the paper, we consider a kinetic approach where collisions are considered using the multi-particle collision algorithm. Kinetic simulation results at medium and low collisionality are also reported.
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.457-464. ⟨hal-01947205⟩
Dongmei Fan, Yannick Marandet, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.490-496. ⟨10.1002/ctpp.201700216⟩. ⟨hal-02114027⟩ Plus de détails...
The three-dimensional (3D) turbulence code TOKAM3X-EIRENE, coupling the 3D non-isothermal version of TOKAM3X to the EIRENE Monte Carlo solver has been developed with the ability to simulate self-consistently the interactions between large-scale flows and turbulence both in limited and diverted plasmas, including recycling. This is especially important for diverted plasmas, where neutrals play a key role and where the recycling source is strongly dominant. The code package relies on the same interface as the Soledge2D-EIRENE code, which retains state-of-the-art plasma-wall interaction, as well as atomic and molecular physics. In this paper, we present the first results obtained in WEST divertor geometry, in laminar mode, with the aim of verifying the new code package. The divertor density regimes are recovered, and the code results are shown to be consistent with the results of the two-point model, thus opening the way for turbulent simulations.
Dongmei Fan, Yannick Marandet, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.490-496. ⟨10.1002/ctpp.201700216⟩. ⟨hal-02114027⟩
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⟩
M. Valentinuzzi, Giorgio Giorgiani, Y. Marandet, H. Bufferand, G. Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.710-717. ⟨hal-01947244⟩ Plus de détails...
A new neutral fluid code has been developed as a necessary step towards a hybrid fluid/kinetic neutral model, to be used in ITER or DEMO simulations, where part of the divertor will be very collisional for neutrals. The neutral fluid code, which is able to handle complex geometries in view of the coupling to Soledge2D, is tested on plasma backgrounds obtained by Soledge2D-Eirene in WEST geometry, for different divertor regimes, and is found to be in fair agreement with the kinetic Monte Carlo solver Eirene. The differences are due to the simplifications introduced in the fluid model and to the fact that a fluid description is not fully valid in these cases.
M. Valentinuzzi, Giorgio Giorgiani, Y. Marandet, H. Bufferand, G. Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.710-717. ⟨hal-01947244⟩
Nicolas Nace, Patrick Tamain, Camille Baudoin, Hugo Bufferand, Guido Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.497-504. ⟨10.1002/ctpp.201700174⟩. ⟨hal-02115405⟩ Plus de détails...
The impact of magnetic configuration on edge turbulence properties in circular limiter geometry is investigated using TOKAM3X, a three-dimensional (3D), first-principle, fluid code for edge plasma. The theoretical spatial tilting of magnetic shear on turbulence fluctuations is recovered. Magnetic shear is found to generate or enhance poloidal high/low field sides (HFS/LFS) and up/down asymmetries. A simulation mimicking the impact of an X-point on circular limiter geometry leads to the formation of two transport barriers that are stable in time, thus leading to the improvement of core particle confinement and to reduction of radial turbulent transport. The magnetic shear, which also strongly enhances the E × B shear, is responsible for the barrier formation.
Nicolas Nace, Patrick Tamain, Camille Baudoin, Hugo Bufferand, Guido Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.497-504. ⟨10.1002/ctpp.201700174⟩. ⟨hal-02115405⟩
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.511-517. ⟨hal-01947233⟩ Plus de détails...
In this paper, a -E transport model is presented as a turbulence reduction tool for a typical ohmic L-mode discharge plasma in a divertor-configurated tokamak. Taking a Tokamak a configuration variable (TCV) study case, a feedback loop procedure is performed using the SolEdge2D code to acquire plasma diffusivity at the outer mid-plane. The -E model is calibrated through its free parameters with the aim of recovering the diffusivity calculated in the feedback procedure. Finally, it is shown that the model can self-consistently calculate diffusivity in the whole domain, recovering the poloidal asymmetries due to interchange instabilities.
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.511-517. ⟨hal-01947233⟩
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.457-464. ⟨10.1002/ctpp.201700222⟩. ⟨hal-02113953⟩ Plus de détails...
In order to improve the presently used ad hoc flux limiter treatment of parallel heat flux transport in edge plasma fluid codes, here, we consider a generalized version of the Fourier law implementing a non-local kernel for the heat flux computation. The Bohm boundary condition at the wall is recovered, introducing a volumetric loss term representing the contribution of suprathermal particles to the energy out flux. As expected, this contribution is negligible in the strongly collisional regime, while it becomes more and more dominant for marginally and low-collisional regimes. In the second part of the paper, we consider a kinetic approach where collisions are considered using the multi-particle collision algorithm. Kinetic simulation results at medium and low collisionality are also reported.
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.457-464. ⟨10.1002/ctpp.201700222⟩. ⟨hal-02113953⟩
Laurent Valade, Annika Ekedahl, Philippe Ghendrih, Yanick Sarazin, Yuuichi Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02116142⟩ Plus de détails...
Hotspot generation by lower-hybrid (LH) launchers is found to be governed by a resonance in the plasma electric field response to the external drive. The kinetic analysis in 1D-1V in the parallel direction allows one to compute the amplification effect for small amplitude of the external drive. The resonant Lorentzian response distorts the distribution function. An island structure is formed in the suprathermal part at the phase velocity of the external electrostatic drive. The non-linear features enhance the plasma response, driving overlap effects between multiple waves at rather low amplitude. The onset of a plateau in the distribution function, with extent reaching one thermal velocity, is already obtained when the standard overlap condition is achieved. The sensitivity of the resonance to plasma parameters and large variation of the amplification magnitude can compensate the fast radial decay of the small-scale features generated by the LH launchers, which are responsible for the interaction with the cold electrons. This mechanism can trigger hotspot generation further in the scrape-off layer than otherwise expected.
Laurent Valade, Annika Ekedahl, Philippe Ghendrih, Yanick Sarazin, Yuuichi Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02116142⟩
Nicolas Nace, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.497-504. ⟨hal-01947228⟩ Plus de détails...
The impact of magnetic configuration on edge turbulence properties in circular limiter geometry is investigated using TOKAM3X, a three-dimensional (3D), first-principle, fluid code for edge plasma. The theoretical spatial tilting of magnetic shear on turbulence fluctuations is recovered. Magnetic shear is found to generate or enhance poloidal high/low field sides (HFS/LFS) and up/down asymmetries. A simulation mimicking the impact of an X-point on circular limiter geometry leads to the formation of two transport barriers that are stable in time, thus leading to the improvement of core particle confinement and to reduction of radial turbulent transport. The magnetic shear, which also strongly enhances the E x B shear, is responsible for the barrier formation.
Nicolas Nace, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.497-504. ⟨hal-01947228⟩
Hugo Bufferand, Guido Ciraolo, Pierfrancesco Di Cintio, Nicolas Fedorczak, Philippe Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.563-569. ⟨10.1002/ctpp.201700162⟩. ⟨hal-02112673⟩ Plus de détails...
The non-local expression proposed by Luciani-Mora-Virmont is implemented in a one dimensional fluid model for the scrape-off layer. Analytical solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The non-local heat flux is compared to the Spitzer-Härm heat flux for different collisionality. KEYWORDS heat conduction, non-local transport, plasma physics 1 INTRODUCTION At the entrance of the scrape-off layer, the plasma collisionality í µí¼ ⋆ defined as the ratio between the field line length and collision mean free path is found to be of order unity. Despite this low collisionality, the tokamak edge plasma modelling relies mostly on the fluid approach and collisional closures that are theoretically only valid at high collisionality. Departure between Braginskii fluid description and kinetic modelling has been highlighted, particularly an underestimation of temperature gradient by the fluid approach. [1] Several kinetic corrections have been proposed to improve the plasma description at intermediate collisionality. [2-5] In this contribution, we investigate kinetic corrections to the local Spitzer-Härm (Braginskii) closure for the heat flux; more precisely, we focus on applying the non-local expression for the heat flux proposed by Luciani-Mora-Virmont [6] to scrape-off layer physics. In particular, we adapt boundary conditions and implement the non-local expression into a 1D hydrodynamic model for the scrape-off layer.
Hugo Bufferand, Guido Ciraolo, Pierfrancesco Di Cintio, Nicolas Fedorczak, Philippe Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.563-569. ⟨10.1002/ctpp.201700162⟩. ⟨hal-02112673⟩
Matteo Valentinuzzi, Giorgio Giorgiani, Yannick Marandet, Hugo Bufferand, Guido Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.710-717. ⟨10.1002/ctpp.201700211⟩. ⟨hal-02116176⟩ Plus de détails...
A new neutral fluid code has been developed as a necessary step towards a hybrid fluid/kinetic neutral model, to be used in ITER or DEMO simulations, where part of the divertor will be very collisional for neutrals. The neutral fluid code, which is able to handle complex geometries in view of the coupling to Soledge2D, is tested on plasma backgrounds obtained by Soledge2D‐Eirene in WEST geometry, for different divertor regimes, and is found to be in fair agreement with the kinetic Monte Carlo solver Eirene. The differences are due to the simplifications introduced in the fluid model and to the fact that a fluid description is not fully valid in these cases.
Matteo Valentinuzzi, Giorgio Giorgiani, Yannick Marandet, Hugo Bufferand, Guido Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.710-717. ⟨10.1002/ctpp.201700211⟩. ⟨hal-02116176⟩
D.-M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.490-496. ⟨hal-01947222⟩ Plus de détails...
The three-dimensional (3D) turbulence code TOKAM3X-EIRENE, coupling the 3D non-isothermal version of TOKAM3X to the EIRENE Monte Carlo solver has been developed with the ability to simulate self-consistently the interactions between large-scale flows and turbulence both in limited and diverted plasmas, including recycling. This is especially important for diverted plasmas, where neutrals play a key role and where the recycling source is strongly dominant. The code package relies on the same interface as the Soledge2D-EIRENE code, which retains state-of-the-art plasma-wall interaction, as well as atomic and molecular physics. In this paper, we present the first results obtained in WEST divertor geometry, in laminar mode, with the aim of verifying the new code package. The divertor density regimes are recovered, and the code results are shown to be consistent with the results of the two-point model, thus opening the way for turbulent simulations.
D.-M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.490-496. ⟨hal-01947222⟩
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.511-517. ⟨10.1002/ctpp.201700163⟩. ⟨hal-02111708⟩ Plus de détails...
In this paper, a κ−ϵ transport model is presented as a turbulence reduction tool for a typical ohmic L‐mode discharge plasma in a divertor‐configurated tokamak. Taking a Tokamak à configuration variable (TCV) study case, a feedback loop procedure is performed using the SolEdge2D code to acquire plasma diffusivity at the outer mid‐plane. The κ−ϵ model is calibrated through its free parameters with the aim of recovering the diffusivity calculated in the feedback procedure. Finally, it is shown that the model can self‐consistently calculate diffusivity in the whole domain, recovering the poloidal asymmetries due to interchange instabilities.
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2018, 58 (6-8), pp.511-517. ⟨10.1002/ctpp.201700163⟩. ⟨hal-02111708⟩
Antoine Briard, Benoît-Joseph Gréa, Vincent Mons, Claude Cambon, Thomas Gomez, et al.. Advanced spectral anisotropic modelling for shear flows. Journal of Turbulence, Taylor & Francis, 2018, 19 (7), pp.570 - 599. ⟨10.1080/14685248.2018.1478092⟩. ⟨hal-01875684⟩ Plus de détails...
In this work, the spectral modelling developed in MCS [Mons, Cambon, Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically-averaged descriptors. J Fluid Mech. 2016;788:147-182] for shear-driven turbulence is further analysed and then improved. First, using self-similarity arguments, it is shown that the asymptotic kinetic energy exponential growth rate is independent of the large scales infrared slope sigma, with, unlike unstably stratified homogeneous turbulence where strongly depends on sigma. The MCS model relies on the truncation at the second order of the spectral two-point velocity correlation expansion into spherical harmonics. The expansion is here pursued at the next even order, the fourth one: the noteworthy consequence is that is decreased compared to MCS and is thus closer to values obtained in direct numerical simulations and experiments. Finally, some analytical considerations about odd-order contributions in the expansion of polarisation anisotropy are proposed.
Antoine Briard, Benoît-Joseph Gréa, Vincent Mons, Claude Cambon, Thomas Gomez, et al.. Advanced spectral anisotropic modelling for shear flows. Journal of Turbulence, Taylor & Francis, 2018, 19 (7), pp.570 - 599. ⟨10.1080/14685248.2018.1478092⟩. ⟨hal-01875684⟩
Antoine Briard, Benoît-Joseph Gréa, Vincent Mons, Claude Cambon, Thomas Gomez, et al.. Advanced spectral anisotropic modelling for shear flows. Journal of Turbulence, Taylor & Francis, 2018, 19 (7), pp.570-599. ⟨10.1080/14685248.2018.1478092⟩. ⟨hal-02112204⟩ Plus de détails...
In this work, the spectral modelling developed in MCS [Mons, Cambon, Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically-averaged descriptors. J Fluid Mech. 2016;788:147-182] for shear-driven turbulence is further analysed and then improved. First, using self-similarity arguments, it is shown that the asymptotic kinetic energy exponential growth rate is independent of the large scales infrared slope sigma, with, unlike unstably stratified homogeneous turbulence where strongly depends on sigma. The MCS model relies on the truncation at the second order of the spectral two-point velocity correlation expansion into spherical harmonics. The expansion is here pursued at the next even order, the fourth one: the noteworthy consequence is that is decreased compared to MCS and is thus closer to values obtained in direct numerical simulations and experiments. Finally, some analytical considerations about odd-order contributions in the expansion of polarisation anisotropy are proposed.
Antoine Briard, Benoît-Joseph Gréa, Vincent Mons, Claude Cambon, Thomas Gomez, et al.. Advanced spectral anisotropic modelling for shear flows. Journal of Turbulence, Taylor & Francis, 2018, 19 (7), pp.570-599. ⟨10.1080/14685248.2018.1478092⟩. ⟨hal-02112204⟩
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. An explicit power-law-based wall model for lattice Boltzmann method–Reynolds-averaged numerical simulations of the flow around airfoils. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065111. ⟨10.1063/1.5031764⟩. ⟨hal-02116210⟩ Plus de détails...
In this paper, an explicit wall model based on a power-law velocity profile is proposed for the simulation of the incompressible flow around airfoils at high Reynolds numbers. This wall model is particularly suited for the wall treatment involved in Cartesian grids. Moreover, it does not require an iterative procedure for the friction velocity determination. The validation of this power-law wall model is assessed for Reynolds-averaged Navier-Stokes simulations of the flow around a two-dimensional airfoil using the lattice Boltzmann approach along with the Spalart-Allmaras turbulence model. Good results are obtained for the prediction of the aerodynamic coefficients and the pressure profiles at two Reynolds numbers and several angles of attack. The explicit power-law is thus well suited for a simplified near-wall treatment at high Reynolds numbers using Cartesian grids.
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. An explicit power-law-based wall model for lattice Boltzmann method–Reynolds-averaged numerical simulations of the flow around airfoils. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065111. ⟨10.1063/1.5031764⟩. ⟨hal-02116210⟩
Mathieu Catchirayer, Jean-François Boussuge, Pierre Sagaut, Marc Montagnac, Dimitrios Papadogiannis, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-02112722⟩ Plus de détails...
Wall-modeling is required to make large-eddy simulations of high-Reynolds number wall-bounded turbulent flows feasible in terms of computational cost. Here, an extension of the integral wall-model for large-eddy simulations (iWMLESs) for incompressible flows developed by Yang et al. ["Integral wall model for large eddy simulations of wall-bounded turbulent flows," Phys. Fluids 27(2), 025112 (2015)] to compressible and isothermal flows is proposed and assessed. The iWMLES approach is analogous to the von Karman-Pohlhausen integral method for laminar flows: the velocity profile is parameterized, and unknown coefficients are determined by matching boundary conditions obeying the integral boundary layer momentum equation. It allows non-equilibrium effects such as pressure gradient and convection to be included at a computing cost similar to analytical wall-models. To take into account density variations and temperature gradients, the temperature profile is also parameterized and the integral compressible boundary layer energy equation is considered. Parameterized profiles are based on the usual logarithmic wall functions with corrective terms to extend their range of validity. Instead of solving a set of differential equations as wall-models based on the thin boundary layer equation approach, a simple linear system is solved. The proposed wall-model is implemented in a finite-volume cell-centered structured grid solver and assessed on adiabatic and isothermal plane channel flows at several friction Reynolds and Mach numbers. For low Mach number cases, mean profiles, wall fluxes, and turbulent fluctuations are in agreement with those of Direct Numerical Simulation (DNS). For supersonic flows, the results are in good agreement with the DNS data, especially the mean velocity quantities and the wall friction, while standard analytical wall-models show their limits.
Mathieu Catchirayer, Jean-François Boussuge, Pierre Sagaut, Marc Montagnac, Dimitrios Papadogiannis, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-02112722⟩
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. An explicit power-law-based wall model for lattice Boltzmann method–Reynolds-averaged numerical simulations of the flow around airfoils. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065111. ⟨10.1063/1.5031764⟩. ⟨hal-01875635⟩ Plus de détails...
In this paper, an explicit wall model based on a power-law velocity profile is proposed for the simulation of the incompressible flow around airfoils at high Reynolds numbers. This wall model is particularly suited for the wall treatment involved in Cartesian grids. Moreover, it does not require an iterative procedure for the friction velocity determination. The validation of this power-law wall model is assessed for Reynolds-averaged Navier-Stokes simulations of the flow around a two-dimensional airfoil using the lattice Boltzmann approach along with the Spalart-Allmaras turbulence model. Good results are obtained for the prediction of the aerodynamic coefficients and the pressure profiles at two Reynolds numbers and several angles of attack. The explicit power-law is thus well suited for a simplified near-wall treatment at high Reynolds numbers using Cartesian grids.
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. An explicit power-law-based wall model for lattice Boltzmann method–Reynolds-averaged numerical simulations of the flow around airfoils. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065111. ⟨10.1063/1.5031764⟩. ⟨hal-01875635⟩
Jean-François Boussuge, Mathieu Catchirayer, J.-F Boussuge, Pierre Sagaut, Marc Montagnac, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-02112710⟩ Plus de détails...
Wall-modeling is required to make large-eddy simulations of high-Reynolds number wall-bounded turbulent flows feasible in terms of computational cost. Here, an extension of the integral wall-model for large-eddy simulations (iWMLESs) for incompressible flows developed by Yang et al. ["Integral wall model for large eddy simulations of wall-bounded turbulent flows," Phys. Fluids 27(2), 025112 (2015)] to compressible and isothermal flows is proposed and assessed. The iWMLES approach is analogous to the von Karman-Pohlhausen integral method for laminar flows: the velocity profile is parameterized, and unknown coefficients are determined by matching boundary conditions obeying the integral boundary layer momentum equation. It allows non-equilibrium effects such as pressure gradient and convection to be included at a computing cost similar to analytical wall-models. To take into account density variations and temperature gradients, the temperature profile is also parameterized and the integral compressible boundary layer energy equation is considered. Parameterized profiles are based on the usual logarithmic wall functions with corrective terms to extend their range of validity. Instead of solving a set of differential equations as wall-models based on the thin boundary layer equation approach, a simple linear system is solved. The proposed wall-model is implemented in a finite-volume cell-centered structured grid solver and assessed on adiabatic and isothermal plane channel flows at several friction Reynolds and Mach numbers. For low Mach number cases, mean profiles, wall fluxes, and turbulent fluctuations are in agreement with those of Direct Numerical Simulation (DNS). For supersonic flows, the results are in good agreement with the DNS data, especially the mean velocity quantities and the wall friction, while standard analytical wall-models show their limits.
Jean-François Boussuge, Mathieu Catchirayer, J.-F Boussuge, Pierre Sagaut, Marc Montagnac, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-02112710⟩
M. Catchirayer, J.-F. Boussuge, Pierre Sagaut, M. Montagnac, D. Papadogiannis, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-01875631⟩ Plus de détails...
Wall-modeling is required to make large-eddy simulations of high-Reynolds number wall-bounded turbulent flows feasible in terms of computational cost. Here, an extension of the integral wall-model for large-eddy simulations (iWMLESs) for incompressible flows developed by Yang et al. ["Integral wall model for large eddy simulations of wall-bounded turbulent flows," Phys. Fluids 27(2), 025112 (2015)] to compressible and isothermal flows is proposed and assessed. The iWMLES approach is analogous to the von Karman-Pohlhausen integral method for laminar flows: the velocity profile is parameterized, and unknown coefficients are determined by matching boundary conditions obeying the integral boundary layer momentum equation. It allows non-equilibrium effects such as pressure gradient and convection to be included at a computing cost similar to analytical wall-models. To take into account density variations and temperature gradients, the temperature profile is also parameterized and the integral compressible boundary layer energy equation is considered. Parameterized profiles are based on the usual logarithmic wall functions with corrective terms to extend their range of validity. Instead of solving a set of differential equations as wall-models based on the thin boundary layer equation approach, a simple linear system is solved. The proposed wall-model is implemented in a finite-volume cell-centered structured grid solver and assessed on adiabatic and isothermal plane channel flows at several friction Reynolds and Mach numbers. For low Mach number cases, mean profiles, wall fluxes, and turbulent fluctuations are in agreement with those of Direct Numerical Simulation (DNS). For supersonic flows, the results are in good agreement with the DNS data, especially the mean velocity quantities and the wall friction, while standard analytical wall-models show their limits.
M. Catchirayer, J.-F. Boussuge, Pierre Sagaut, M. Montagnac, D. Papadogiannis, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, American Institute of Physics, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-01875631⟩
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⟩
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⟩
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
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-02115828⟩ 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-02115828⟩
Journal: International Journal for Numerical Methods in Fluids
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⟩
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-02115966⟩ 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-02115966⟩
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⟩
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. ⟨10.1016/j.pocean.2017.05.001⟩. ⟨hal-02111578⟩ 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 a 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 a hydropower plant (250 m 3 /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/h and a hydropower runoff of 250 m 3 /s. 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 (where BSS = 0). When comparing the BSS value at the four control points with the critical value, BSS cr , at which the sediment mobility would occur, we see that for the smaller bottom roughness values (ranging from z 0 = 3.5 Â 10 À4 mm, to 3.5 Â 10 À2 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 BSS cr-at least for the silt sediments (ranging from z 0 = 3.5 Â 10 À4 mm, to 3.5 Â 10 À3 mm). This confirms the possibility that the coastal jet could be a stressor for SAV replanting.
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. ⟨10.1016/j.pocean.2017.05.001⟩. ⟨hal-02111578⟩
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⟩
D Rigamonti, L. Giacomelli, G Gorini, M. Nocente, M. Rebai, et al.. Neutron spectroscopy measurements of 14 MeV neutrons at unprecedented energy resolution and implications for deuterium–tritium fusion plasma diagnostics. Measurement Science and Technology, IOP Publishing, 2018, 29 (4), pp.045502. ⟨10.1088/1361-6501/aaa675⟩. ⟨hal-02177077⟩ Plus de détails...
An accurate calibration of the JET neutron diagnostics with a 14 MeV neutron generator was performed in the first half of 2017 in order to provide a reliable measurement of the fusion power during the next JET deuterium-tritium (DT) campaign. In order to meet the target accuracy, the chosen neutron generator has been fully characterized at the Neutron Metrology Laboratory of the National Physical Laboratory (NPL), Teddington, United Kingdom. The present paper describes the measurements of the neutron energy spectra obtained using a high-resolution single-crystal diamond detector (SCD). The measurements, together with a new neutron source routine 'ad hoc' developed for the MCNP code, allowed the complex features of the neutron energy spectra resulting from the mixed D/T beam ions interacting with the T/D target nuclei to be resolved for the first time. From the spectral analysis a quantitative estimation of the beam ion composition has been made. The unprecedented intrinsic energy resolution (<1% full width at half maximum (FWHM) at 14 MeV) of diamond detectors opens up new prospects for diagnosing DT plasmas, such as, for instance, the possibility to study non-classical slowing down of the beam ions by neutron spectroscopy on ITER.
D Rigamonti, L. Giacomelli, G Gorini, M. Nocente, M. Rebai, et al.. Neutron spectroscopy measurements of 14 MeV neutrons at unprecedented energy resolution and implications for deuterium–tritium fusion plasma diagnostics. Measurement Science and Technology, IOP Publishing, 2018, 29 (4), pp.045502. ⟨10.1088/1361-6501/aaa675⟩. ⟨hal-02177077⟩
Sylvain Chateau, Umberto d'Ortona, Sébastien Poncet, Julien Favier. Transport and Mixing Induced by Beating Cilia in Human Airways. Frontiers in Physiology, Frontiers, 2018, 9, pp.161. ⟨10.3389/fphys.2018.00161⟩. ⟨hal-01875672⟩ Plus de détails...
The fluid transport and mixing induced by beating cilia, present in the bronchial airways, are studied using a coupled lattice Boltzmann-Immersed Boundary solver. This solver allows the simulation of both single and multi-component fluid flows around moving solid boundaries. The cilia aremodeled by a set of Lagrangian points, and Immersed Boundary forces are computed onto these points in order to ensure the no-slip velocity conditions between the cilia and the fluids. The cilia are immersed in a two-layer environment: the periciliary layer (PCL) and the mucus above it. The motion of the cilia is prescribed, as well as the phase lag between two cilia in order to obtain a typical collective motion of cilia, known as metachronal waves. The results obtained from a parametric study show that antiplectic metachronal waves are the most efficient regarding the fluid transport. A specific value of phase lag, which generates the larger mucus transport, is identified. The mixing is studied using several populations of tracers initially seeded into the pericilary liquid, in the mucus just above the PCL-mucus interface, and in the mucus far away from the interface. We observe that each zone exhibits different chaotic mixing properties. The larger mixing is obtained in the PCL layer where only a few beating cycles of the cilia are required to obtain a full mixing, while above the interface, the mixing is weaker and takes more time. Almost no mixing is observed within the mucus, and almost all the tracers do not penetrate the PCL layer. Lyapunov exponents are also computed for specific locations to assess how the mixing is performed locally. Two time scales are introduced to allow a comparison between mixing induced by fluid advection and by molecular diffusion. These results are relevant in the context of respiratory flows to investigate the transport of drugs for patients suffering from chronic respiratory diseases.
Sylvain Chateau, Umberto d'Ortona, Sébastien Poncet, Julien Favier. Transport and Mixing Induced by Beating Cilia in Human Airways. Frontiers in Physiology, Frontiers, 2018, 9, pp.161. ⟨10.3389/fphys.2018.00161⟩. ⟨hal-01875672⟩
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, 72, pp.123-134. ⟨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, 72, pp.123-134. ⟨10.1016/j.euromechflu.2018.03.009⟩. ⟨hal-01789049⟩
Philippe Meliga, Edouard Boujo, Marcelo Meldi, François 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, 72, pp.123-134. ⟨10.1016/j.euromechflu.2018.03.009⟩. ⟨hal-02114650⟩ Plus de détails...
This study assesses the ability of a sensitivity-based, span-wise homogeneous control velocity distributed at the surface of a circular cylinder to cut down the cost of reducing drag by more classical techniques, e.g., base bleed and lateral suction. At Reynolds number Re = 100, achieving the linear optimal reduction requires a time-dependent control velocity, set at each time instant against the sensitivity of the instantaneous drag. This approach however fails against even small control amplitudes because the system does not have time to adjust to the rapid change in the value of the wall velocity, and drag essentially increases. An eﬃcient (albeit linearly suboptimal) reduction is however achieved using a steady control velocity set against the time averaged sensitivity. By doing so, drag decreases monotonically with the control momentum coeﬃcient, and the sensitivity-based design exhibits a signiﬁcant advantage over base bleed and lateral suction, that both reduce drag to a far lesser extent. Similar results are reported using various levels of modeling to compute approximations to the exact, time averaged sensitivity. The mean ﬂow approach, that requires knowledge of the sole time averaged cylinder ﬂow, yields especially promising results given the marginal computational eﬀort. This approach is thus extended to the turbulent case at Re = 3900, where it achieves similar eﬃciency in the frame of both 2-D and 3-D RANS modeling. The study concludes with a discussion about the feasibility to extend the scope to span-wise periodic forcing velocities, following the line of thought of Kim & Choi [Phys. Fluids 17, 033103 (2005)].
Philippe Meliga, Edouard Boujo, Marcelo Meldi, François 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, 72, pp.123-134. ⟨10.1016/j.euromechflu.2018.03.009⟩. ⟨hal-02114650⟩
Eunok Yim, J.-M Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor-stator cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 836, pp.43-71. ⟨10.1017/jfm.2017.771⟩. ⟨hal-02121890⟩ Plus de détails...
This paper proposes a resolution to the conundrum of the roles of convective and absolute instability in transition of the rotating-disk boundary layer. It also draws some comparison with swept-wing flows. Direct numerical simulations based on the incompressible Navier–Stokes equations of the flow over the surface of a rotating disk with modelled roughness elements are presented. The rotating-disk flow has been of particular interest for stability and transition research since the work by Lingwood (J. Fluid Mech., vol. 299, 1995, pp. 17–33) where an absolute instability was found. Here stationary disturbances develop from roughness elements on the disk and are followed from the linear stage, growing to saturation and finally transitioning to turbulence. Several simulations are presented with varying disturbance amplitudes. The lowest amplitude corresponds approximately to the experiment by Imayama et al. (J. Fluid Mech., vol. 745, 2014a, pp. 132–163). For all cases, the primary instability was found to be convectively unstable, and secondary modes were found to be triggered spontaneously while the flow was developing. The secondary modes further stayed within the domain, and an explanation for this is a proposed globally unstable secondary instability. For the low-amplitude roughness cases, the disturbances propagate beyond the threshold for secondary global instability before becoming turbulent, and for the high-amplitude roughness cases the transition scenario gives a turbulent flow directly at the critical Reynolds number for the secondary global instability. These results correspond to the theory of Pier (J. Engng Maths, vol. 57, 2007, pp. 237–251) predicting a secondary absolute instability. In our simulations, high temporal frequencies were found to grow with a large amplification rate where the secondary global instability occurred. For smaller radial positions, low-frequency secondary instabilities were observed, tripped by the global instability. The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor-stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Kármán self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counterclockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers m, in the range m ∈ [32, 78]. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.
Eunok Yim, J.-M Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor-stator cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 836, pp.43-71. ⟨10.1017/jfm.2017.771⟩. ⟨hal-02121890⟩