Plasmas de tokamak: Modélisation, transport turbulent, plasma de bord
Méthodes numériques d'ordre élevé
Publications scientifiques au M2P2
2018
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. 〈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. 〈hal-01946999〉
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
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〉
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〉
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〉
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〉
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, 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〉
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〉
H. Riahi, Marcello Meldi, Julien Favier, Eric Serre, Eric Goncalves da Silva. A pressure-corrected Immersed Boundary Method for the numerical simulation of compressible flows. Journal of Computational Physics, Elsevier, 2018, 374, pp.361-383. 〈10.1016/j.jcp.2018.07.033〉. 〈hal-01859760〉 Plus de détails...
The development of an improved new IBM method is proposed in the present article. This method roots in efficient proposals developed for the simulation of incompressible flows, and it is expanded for compressible configurations. The main feature of this model is the integration of a pressure-based correction of the IBM forcing which is analytically derived from the set of dynamic equations. The resulting IBM method has been integrated in various flow solvers available in the CFD platform OpenFOAM. A rigorous validation has been performed considering different test cases of increasing complexity. The results have been compared with a large number of references available in the literature of experimental and numerical nature. This analysis highlights numerous favorable characteristics of the IBM method, such as precision, flexibility and computational cost efficiency.
H. Riahi, Marcello Meldi, Julien Favier, Eric Serre, Eric Goncalves da Silva. A pressure-corrected Immersed Boundary Method for the numerical simulation of compressible flows. Journal of Computational Physics, Elsevier, 2018, 374, pp.361-383. 〈10.1016/j.jcp.2018.07.033〉. 〈hal-01859760〉
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. 〈10.1016/j.cma.2018.05.032〉. 〈hal-01865708〉 Plus de détails...
In this paper a Powell–Sabin finite-element (PS-FEM) 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 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.
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. 〈10.1016/j.cma.2018.05.032〉. 〈hal-01865708〉
Journal: Computer Methods in Applied Mechanics and Engineering
Denis Martinand, Eric Serre, Richard M. Lueptow. Linear and weakly nonlinear analyses of cylindrical Couette flow with axial and radial flows. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 824, pp.438 - 476. 〈10.1017/jfm.2017.351〉. 〈hal-01592948〉 Plus de détails...
Extending previous linear stability analyses of the instabilities developing in permeable Taylor-Couette-Poiseuille flows where axial and radial throughflows are superimposed on the usual Taylor-Couette flow, we further examine the linear behaviour and expand the analysis to consider the weakly nonlinear behaviour of convective-type instabilities by means of the derivation of the fifth-order amplitude equation together with direct numerical simulations. Special attention is paid to the influence of the radius ratio eta = r(in)/r(out), and particularly to wide gaps (small eta) and how they magnify the effects of the radial flow. The instabilities take the form of pairs of counter-rotating toroidal vortices superseded by helical ones as the axial flow is increased. Increasing the radial inflow draws these vortices near the inner cylinder, where they shrink relative to the annular gap, when this gap is wide. Strong axial and radial flows in a narrow annular gap lead to a very large azimuthal wavenumber with steeply sloped helical vortices. Strong radial outflow in a wide annular gap results in very large helical vortices. The analytical and numerical saturated vortices match quite well. In addition, radial inflows or outflows can turn the usually supercritical bifurcation from laminar to vortical flow into a subcritical one. The radial flow above which this change occurs decreases as the radius ratio eta decreases. A practical motivation for this weakly nonlinear analysis is found in modelling dynamic filtration devices, which rely on vortical instabilities to reduce the processes of accumulation on their membranes.
Denis Martinand, Eric Serre, Richard M. Lueptow. Linear and weakly nonlinear analyses of cylindrical Couette flow with axial and radial flows. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 824, pp.438 - 476. 〈10.1017/jfm.2017.351〉. 〈hal-01592948〉
W.A. Gracias, P. Tamain, Eric Serre, R.A. Pitts, L. Garcia. The impact of magnetic shear on the dynamics of a seeded 3D filament in slab geometry. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.798 - 807. 〈10.1016/j.nme.2017.02.022〉. 〈hal-01702187〉 Plus de détails...
Seeded filament simulations are used to study blob dynamics with the state-of-the-art TOKAM3X fluid code in the scrape-off layer (SOL) using a slab geometry. The filamentary dynamics recovered with the code are compared with previously predicted analytical blob velocity scalings while also studying the effect of field line pitch angle on these dynamics and are found to be similar. The effect of changing magnetic topology on filamentary motion is also investigated. Magnetic shear is introduced in the model by the sudden and localised variation of field line pitch angle for a narrow radially located region constituting effectively a shearing zone. Three such shear zones are tested to see how they affect filament motion. Filaments are initialised radially upstream from the shear zone and recorded as they convect towards the far-SOL side. The lowest intensity shear zone allows many of the higher amplitude filaments to pass through after dampening them. On the other hand, the highest intensity shear zones prevent all filaments from progressing to the wall beyond the shear zone and, in certain cases for high density amplitude filaments, is able to generate a new filament downstream from the shear zone.
W.A. Gracias, P. Tamain, Eric Serre, R.A. Pitts, L. Garcia. The impact of magnetic shear on the dynamics of a seeded 3D filament in slab geometry. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.798 - 807. 〈10.1016/j.nme.2017.02.022〉. 〈hal-01702187〉
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.931 - 934. 〈10.1016/j.nme.2017.02.007〉. 〈hal-01702229〉 Plus de détails...
Transport codes are the main workhorses for global edge studies and modern divertor design. These tools do not resolve turbulent fluctuations responsible for the bulk of cross-field transport in the Scrape-off Layer (SOL), and solve mean field equations instead. Turbulent fluxes are modelled by diffusive transport along the gradients of the mean fields. Improvements of this description, on the basis of approaches developed in computational fluid dynamics are discussed, broadening the outlook given in Bufferand et al. (2016) [10]. This contribution focuses on additional closure issues related to non-linearities in sources/sinks from plasma-wall interactions, here sputtered fluxes from the plasma facing components. “Fluctuation dressed” sputtering yields Yeff are introduced and calculated from turbulence simulations. Properly taking fluctuations into account is shown to lead to higher sputtering at sub-threshold energies compared to mean field predictions. As a first step towards an implementation in a transport code, the possibility of parametrizing Yeff in terms of the mean fields is tentatively investigated.
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.931 - 934. 〈10.1016/j.nme.2017.02.007〉. 〈hal-01702229〉
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.1171 - 1177. 〈10.1016/j.nme.2016.12.022〉. 〈hal-01702267〉 Plus de détails...
Motivated by Radio Frequency (RF) heating studies, the response of the plasma of tokamaks to the presence of a locally polarized limiter is studied. In a first part, we use the TOKAM3X 3D global edge turbulence code to analyse the impact of such biasing in a realistic geometry. Key features of experimental observations are qualitatively recovered, especially the extension of a potential and density perturbation on long, but finite, distances along connected field lines. The perturbation is also found to extend in the transverse direction. Both observations demonstrate the influence of perpendicular current loops on the plasma confirming the need for an accurate description in reduced models. In a second part, we use the TOKAM2D slab turbulence code to determine the validity of using a transverse Ohm's law for this purpose. Results indicate that a local Ohm's law with a constant and uniform perpendicular resistivity appears at least as an oversimplified description of perpendicular charge transport in a turbulent Scrape-Off Layer.
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.1171 - 1177. 〈10.1016/j.nme.2016.12.022〉. 〈hal-01702267〉
Eddy Constant, Julien Favier, Marcello Meldi, Philippe Meliga, Eric Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers and Fluids, Elsevier, 2017, 157, pp.55 - 72. 〈10.1016/j.compfluid.2017.08.001〉. 〈hal-01591562〉 Plus de détails...
The present work proposes a modified Pressure-Implicit Split-Operator (PISO) solver integrating the recent Immersed Boundary Method (IBM) proposed by Pinelli et al. [1] in order to perform reliable simulations of incompressible flows around bluff bodies using the open source toolbox OpenFOAM version 2.2 (ESI-OpenCFD [2]). The (IBM) allows for a precise representation of fixed and moving solid obstacles embedded in the physical domain, using uniform or stretched Cartesian meshes. Owing to this feature, the maximum level of accuracy and scalability of the numerical solvers can be systematically achieved. An iterative scheme based on sub-iterations between (IBM) and pressure correction has been implemented in the native (PISO) solver of OpenFOAM. This allows one to use fast optimized Poisson solvers while satisfying simultaneously the divergence-free flow state and the no-slip condition at the body surface. To compute the divergence of the momentum equation (in the PISO loop) and the interpolation of the fluxes, we propose an hybrid calculation with an analytical resolution (using the kernel function equation) of the quantities involving the force term (singular quantities). A careful and original verification study has been carried out which allows to estimate three different errors related to the discretization and to the (IBM). Various 2D and 3D well-documented test cases of academic flows around fixed or moving cylinders have been simulated and carefully validated against existing data from the literature in a large range of Reynolds numbers, Re = 30 − 3900 and in the frame of DNS and DDES OpenFOAM native models.
Eddy Constant, Julien Favier, Marcello Meldi, Philippe Meliga, Eric Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers and Fluids, Elsevier, 2017, 157, pp.55 - 72. 〈10.1016/j.compfluid.2017.08.001〉. 〈hal-01591562〉
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.953 - 958. 〈10.1016/j.nme.2017.01.008〉. 〈hal-01702255〉 Plus de détails...
The flux expansion effect on the Scrape-Off Layer equilibrium is inspected through TOKAM3X 3D turbulence simulations. Three magnetic equilibria with analytically controlled flux expansion are built, representing respectively a positive, a null and a negative Shafranov shift. Turbulent E × B fluxes across flux surfaces show similar amplitudes and poloidal distributions in all cases. The ballooning nature of the interchange instability is recovered, with an enhancement of turbulence in the vicinity of the limiter, probably due to a Kelvin–Helmoltz instability. Interestingly, the poloidally averaged density decay length is found to be shorter almost by a factor 2 in the case of flux surfaces compressed at the low-field side midplane, with respect to the opposite case, indicating the presence of unfavorable conditions for the turbulent transport. The difference in the magnetic field line shape is pointed out as a mechanism which affects the turbulent transport across the flux surfaces. Indeed the unstable region has a larger parallel extension when flux expansion in the low-field side is larger. Moreover, the configuration with a lower magnetic shear at the low-field side midplane shows a more unstable behavior. The role of this parameter in turbulence stabilization is qualitatively evaluated. The difference in the distribution of transport along the parallel direction is shown to affect also the parallel flows, which are analyzed for the three proposed cases.
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.953 - 958. 〈10.1016/j.nme.2017.01.008〉. 〈hal-01702255〉
H. Bufferand, C. Baudoin, J. Bucalossi, G. Ciraolo, J. Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D–EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.852 - 857. 〈10.1016/j.nme.2016.11.031〉. 〈hal-01702275〉 Plus de détails...
In order to improve cross-field transport description, drifts and currents have been implemented in SOLEDGE2D–EIRENE. The derivation of an equation for the electric potential is recalled. The resolution of current equation is tested in a simple slab case. WEST divertor simulations in forward-B and reverse-B fields are also discussed. A significant increase of ExB shear is observed in the forward-B configuration that could explain a favorable L-H transition in this case.
H. Bufferand, C. Baudoin, J. Bucalossi, G. Ciraolo, J. Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D–EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.852 - 857. 〈10.1016/j.nme.2016.11.031〉. 〈hal-01702275〉
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.187 - 192. 〈10.1016/j.nme.2016.12.025〉. 〈hal-01702237〉 Plus de détails...
Simulations of WEST H-mode divertor scenarios have been performed with SOLEDGE2D-EIRENE edge plasma transport code, both for pure deuterium and nitrogen seeded discharge. In the pure deuterium case, a target heat flux of 8 MW/m2 is reached, but misalignment between heat and the particle outflux yields 50 eV plasma temperature at the target plates. With nitrogen seeding, the heat and particle outflux are observed to be aligned so that lower plasma temperatures at the target plates are achieved together with the required high heat fluxes. This change in heat and particle outflux alignment is analysed with respect to the role of divertor geometry and the impact of vertical vs horizontal target plates on neutrals spreading.
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, Elsevier, 2017, 12, pp.187 - 192. 〈10.1016/j.nme.2016.12.025〉. 〈hal-01702237〉
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, IOP Publishing, 2017, 57 (3), pp.036029. 〈10.1088/1741-4326/aa5332〉. 〈hal-01592945〉 Plus de détails...
The poloidal asymmetries of parallel flows in edge plasmas are investigated by the 3D fluid turbulence code TOKAM3X. A diverted COMPASS-like magnetic equilibrium is used for the simulations. The measurements and simulations of parallel Mach numbers are compared, and exhibit good qualitative agreement. Small-scale turbulent transport is observed to dominate near the low field side midplane, even though it co-exists with significant large-scale cross-field fluxes. Despite the turbulent nature of the plasma in the divertor region, simulations show the low effectiveness of turbulence for the cross-field transport towards the private flux region. Nevertheless, a complex pattern of fluxes associated with the average field components are found to cross the separatrix in the divertor region. Large-scale and small-scale turbulent E x B transport, along with the del B drift, drive the asymmetries in parallel flows. A semian-alytical model based on mass and parallel momentum balances allows the poloidal drift effects on the asymmetry pattern to be evaluated. As in the experiments, a reversed B-T simulation provides a way of self-consistently separating the effects of turbulent transport and large-scale flows, which must be reversed for a reversed field. The large-scale contribution is found to be responsible for typically 50% of the effect on the Mach number, evaluated at the top of the machine. The presented picture shows the complex interplay between drifts and turbulence, underlining the necessity of a global approach to edge plasma modelling, including a self-consistent description of the turbulence.
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, IOP Publishing, 2017, 57 (3), pp.036029. 〈10.1088/1741-4326/aa5332〉. 〈hal-01592945〉
R.J.A. Howard, Eric Serre. Large eddy simulation in Code_Saturne of thermal mixing in a T junction with brass walls. International Journal of Heat and Fluid Flow, Elsevier, 2017, 63, pp.119 - 127. 〈10.1016/j.ijheatfluidflow.2016.09.011〉. 〈hal-01592931〉 Plus de détails...
Following on from Kuhn et al (2010) we study the capability of large eddy simulation with conjugate heat transfer to predict thermal fluctuations with thermal mixing. Wall functions are used to model the wall heat transfer. Comparison with experimental results show that the temperature variance on the outer skin of the solid is well predicted by the simulation. It is shown that the variance of thermal flux in the fluid closely maps the temperature variance at the outer boundary of the solid. Since the variance of thermal flux is closely related to the dissipation of temperature variance it can be concluded that the dissipation of temperature variance in the fluid is linked to temperature variance in the solid. Analysis of the equation of the temperature variance in the solid confirms this is indeed the case. It is the dissipation of temperature variance in the fluid that characterizes how the temperature variance penetrates the solid. Thus RANS modelling can be used to predict thermal variance in solids provided that there is an accurate model for the dissipation of temperature variance at the wall and an equation for the thermal variance in the solid is solved.
R.J.A. Howard, Eric Serre. Large eddy simulation in Code_Saturne of thermal mixing in a T junction with brass walls. International Journal of Heat and Fluid Flow, Elsevier, 2017, 63, pp.119 - 127. 〈10.1016/j.ijheatfluidflow.2016.09.011〉. 〈hal-01592931〉
Journal: International Journal of Heat and Fluid Flow
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, In press. 〈hal-01655295〉 Plus de détails...
The nonlocal expression proposed by Luciani-Mora-Virmont is implemented into a 1D fluid model for the scrape-off layer. Analytic solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The nonlocal heat flux is compared to Spitzer-Härm heat flux for different collisionality.
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, Wiley-VCH Verlag, In press. 〈hal-01655295〉
Philippe Meliga, Olivier Cadot, Eric Serre. Experimental and Theoretical Sensitivity Analysis of Turbulent Flow Past a Square Cylinder. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2016, 97 (4, SI), pp.987-1015. 〈10.1007/s10494-016-9755-0〉. 〈hal-01461791〉 Plus de détails...
We assess experimentally and theoretically the ability of a small control cylinder to alter vortex shedding in turbulent flow past a square cylinder at R e = 22,000. Results are presented in terms of sensitivity maps showing the flow regions where the shedding frequency and amplitude are most affected by the control cylinder. Experimental results are obtained for a ratio 0.02 of the cylinder diameters, over an extended domain covering the wake, the shear layers and the free stream. The shedding frequency can be either decreased or increased, the largest effects being obtained placing the control cylinder at the outer edge of the detached shear layers (associated with frequency decrease) or upstream of the square cylinder (associated with frequency increase, in contrast with previous results obtained for a D-shaped geometry of the main cylinder). In contrast, the oscillation amplitude is rarely decreased, meaning that any variation of the shedding frequency comes at the expense of more intense vortex shedding. These findings are revisited in the frame of a theoretical, linear sensitivity analysis of the time-averaged mean flow, performed using adjoint methods in the frame of Reynolds-averaged Navier-Stokes modeling. We show that the retained approach carries valuable information in view of guiding efficient control strategy, as it allows identifying the main regions yielding either a decrease or an increase of the shedding frequency in striking agreement with the experiments. This is a tremendous timesaving in so far as the controlled states need not be computed, the overall computational cost being roughly that of computing the mean flow. In contrast, performing the sensitivity analysis on the underlying unstable steady state yields flawed predictions, hence stressing the need to encompass some level of mean coherent-coherent perturbations interaction in the linear model.
Philippe Meliga, Olivier Cadot, Eric Serre. Experimental and Theoretical Sensitivity Analysis of Turbulent Flow Past a Square Cylinder. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2016, 97 (4, SI), pp.987-1015. 〈10.1007/s10494-016-9755-0〉. 〈hal-01461791〉
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, Elsevier, 2016, 321, pp.606-623. 〈10.1016/j.jcp.2016.05.038〉. 〈hal-01461797〉 Plus de détails...
The new code TOKAM3X simulates plasma turbulence in full torus geometry including the open field lines of the Scrape-off Layer (SOL) and the edge closed field lines region in the vicinity of the separatrix. Based on drift-reduced Braginskii equations, TOKAM3X is able to simulate both limited and diverted plasmas. Turbulence is flux driven by incoming particles from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed so that interactions between large scale flows and turbulence are consistently treated. Based on a domain decomposition, specific numerical schemes are proposed using conservative finite-differences associated to a semi-implicit time advancement. The process computation is multi-threaded and based on MPI and OpenMP libraries. In this paper, fluid model equations are presented together with the proposed numerical methods. The code is verified using the manufactured solution technique and validated through documented simple experiments. Finally, first simulations of edge plasma turbulence in X-point geometry are also introduced in a JET geometry. (C) 2016 Elsevier Inc. All rights reserved.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, Elsevier, 2016, 321, pp.606-623. 〈10.1016/j.jcp.2016.05.038〉. 〈hal-01461797〉
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.555-562. 〈10.1002/ctpp.201610033〉. 〈hal-01455239〉 Plus de détails...
Cross-field transport in edge tokamak plasmas is known to be dominated by turbulent transport. A dedicated effort has been made to simulate this turbulent transport from first principle models but the numerical cost to run these simulations on the ITER scale remains prohibitive. Edge plasma transport study relies mostly nowadays on so-called transport codes where the turbulent transport is taken into account using effective ad-hoc diffusion coeffecients. In this contribution, we propose to introduce a transport equation for the turbulence intensity in SOLEDGE2D-EIRENE to describe the interchange turbulence properties. Going beyond the empirical diffusive model, this system automatically generates profiles for the turbulent transport and hence reduces the number of degrees of freedom for edge plasma transport codes. We draw inspiration from the k-epsilon model widely used in the neutral fluid community. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.555-562. 〈10.1002/ctpp.201610033〉. 〈hal-01455239〉
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.575-580. 〈10.1002/ctpp.201610038〉. 〈hal-01455240〉 Plus de détails...
The interplay between Langmuir probes (LP) and Scrape-Off-Layer plasma turbulence is numerically investigated with the TOKAM2D and TOKAM3X fluid codes. The LP is modelled by biasing a part of the target plates surface; we then study its impact on the turbulent transport 1) in presence of electron temperature fluctuations and 2) with a complete description of the parallel dynamics. We find that a biased probe can disturb local plasma parameters as well as turbulent transport in its vicinity, by polarizing the connected flux tube and thus driving a strong ExB vortex. Moreover, electron temperature fluctuations are found to account significantly those of floating potential, but with a limited impact on flux measurements depending on the probe's exact geometry. The 3D study of the problem shows the attenuation, but the persistency, of these perturbations induced by the presence of the LP. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.575-580. 〈10.1002/ctpp.201610038〉. 〈hal-01455240〉
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.569-574. 〈10.1002/ctpp.201610063〉. 〈hal-01455242〉 Plus de détails...
The impact of a 3D localized particle source on the edge plasma in 3D global turbulence simulations is investigated using the TOKAM3X fluid code. Results apply to advanced fueling methods such as Supersonic Molecular Beam Injection (SMBI) or pellets injection. The fueling source is imposed as a volumetric particle source in the simulations so that the physics leading to the ionization of particles and its localization are not taken into account. As already observed in experiments, the localized particle source strongly perturbs both turbulence and the large scale organization of the edge plasma. The localized increase of the pressure generated by the source drives sonic parallel flows in the plasma, leading to a poloidal redistribution of the particles on the time scale of the source duration. However, the particle deposition also drives localized transverse pressure gradients which impacts the stability of the plasma with respect to interchange processes. The resulting radial transport occurs on a sufficiently fast time scale to compete with the parallel redistribution of particles, leading to immediate radial losses of a significant proportion of the injected particles. Low Field Side (LFS) and High Field Side (HFS) injections exhibit different dynamics due to their interaction with curvature. In particular, HFS particle deposition drives an inward flux leading to differences in the particle deposition efficiency (higher for HFS than LFS). These results demonstrate the importance of taking into account plasma transport in a self-consistent manner when investigating fueling methods. ((c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, Wiley-VCH Verlag, 2016, 56 (6-8), pp.569-574. 〈10.1002/ctpp.201610063〉. 〈hal-01455242〉
Fabio Riva, Clothilde Colin, Julien Denis, Luke Easy, Ivo Furno, et al.. Blob dynamics in the TORPEX experiment: a multi-code validation. Plasma Physics and Controlled Fusion, IOP Publishing, 2016, 58 (4), 〈10.1088/0741-3335/58/4/044005〉. 〈hal-01461784〉 Plus de détails...
Three-dimensional and two-dimensional seeded blob simulations are performed with five different fluid models, all based on the drift-reduced Braginskii equations, and the numerical results are compared among themselves and validated against experimental measurements provided by the TORPEX device ( Fasoli et al 2006 Phys. Plasmas 13 055902). The five models are implemented in four simulation codes, typically used to simulate the plasma dynamics in the tokamak scrape-off layer, namely BOUT++ (Dudson et al 2009 Comput. Phys. Commun. 180 1467), GBS (Ricci et al 2012 Plasma Phys. Control. Fusion 54 124047), HESEL (Nielsen et al 2015 Phys. Lett. A 379 3097), and TOKAM3X (Tamain et al 2014 Contrib. Plasma Phys. 54 555). Three blobs with different velocities and different stability properties are simulated. The differences observed among the simulation results and the different levels of agreement with experimental measurements are investigated, increasing our confidence in our simulation tools and shedding light on the blob dynamics. The comparisons demonstrate that the radial blob dynamics observed in the three-dimensional simulations is in good agreement with experimental measurements and that, in the present experimental scenario, the two-dimensional model derived under the assumption of k(vertical bar vertical bar) = 0 is able to recover the blob dynamics observed in the three-dimensional simulations. Moreover, it is found that an accurate measurement of the blob temperature is important to perform reliable seeded blob simulations.
Fabio Riva, Clothilde Colin, Julien Denis, Luke Easy, Ivo Furno, et al.. Blob dynamics in the TORPEX experiment: a multi-code validation. Plasma Physics and Controlled Fusion, IOP Publishing, 2016, 58 (4), 〈10.1088/0741-3335/58/4/044005〉. 〈hal-01461784〉
J. Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, IOP Publishing, 2016, T167, 〈10.1088/0031-8949/T167/1/014073〉. 〈hal-01459103〉 Plus de détails...
A thermal wall model is developed for the SolEdge2D-EIRENE edge transport code for calculating the surface temperature of the actively-cooled vessel components in interaction with the plasma. This is a first step towards a self-consistent evaluation of the recycling of particles, which depends on the wall surface temperature. The proposed thermal model is built to match both steady-state temperature and time constant of actively-cooled plasma facing components. A benchmark between this model and the Finite Element Modelling code CAST3M is performed in the case of an ITER-like monoblock. An example of application is presented for a SolEdge2D-EIRENE simulation of a medium-power discharge in the WEST tokamak, showing the steady-state wall temperature distribution and the temperature cycling due to an imposed Edge Localised Mode-like event.
J. Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, IOP Publishing, 2016, T167, 〈10.1088/0031-8949/T167/1/014073〉. 〈hal-01459103〉
Lyes Bordja, Emilia Arco, Éric Serre, Rachid Bessaih. EFFECTS OF AXIAL MAGNETIC FIELD AND THERMAL CONVECTION ON A COUNTERROTATING VON KARMAN FLOW. Heat Transfer Research, Begell House, 2016, 47 (5), pp.471-488. 〈10.1615/HeatTransRes.2016007441〉. 〈hal-01462070〉 Plus de détails...
The effects of thermal convection and of a constant axial magnetic field on a von Karman flow driven by the exact counter-rotation of two lids are investigated in a vertical cylinder of aspect ratio Gamma(= height/radius) = 2 at a fixed Reynolds number Re(= Omega R-2/v) = 300. Direct numerical simulations are performed when varying separately the Rayleigh and Hartmann numbers in the range [0, 1800] and [0, 20], respectively, in the limit of the Boussinesq approximation and of a small magnetic Reynolds numbers, Re-m << 1. Without a magnetic field, the base flow symmetries of the von Karman flow are broken by thermal convection that becomes dominant in the range of Ra [500, 1000]. Three-dimensional solutions are characterized by the occurrence of a steady, m = 1, azimuthal mode exhibiting a cat's eye vortex in the circumferential plane. When increasing the Rayleigh number in the range [500, 1000], the vortex pulsates in an oscillatory manner, due to variations of the flow intensity. Otherwise, increasing the axial magnetic field intensity stabilizes the flow, and the oscillatory motion can be inhibited. Numerical solutions show that the critical Rayleigh number for transition increases linearly with the Hartmann number. Finally, results show that when varying the Rayleigh number, the structure of the electric potential can be strongly modified by thermal convection. Such an observation suggests new induction mechanisms in the case of small nonzero values of the magnetic Reynolds number.
Lyes Bordja, Emilia Arco, Éric Serre, Rachid Bessaih. EFFECTS OF AXIAL MAGNETIC FIELD AND THERMAL CONVECTION ON A COUNTERROTATING VON KARMAN FLOW. Heat Transfer Research, Begell House, 2016, 47 (5), pp.471-488. 〈10.1615/HeatTransRes.2016007441〉. 〈hal-01462070〉
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, IOP Publishing, 2015, 57 (5), pp.054014. 〈10.1088/0741-3335/57/5/054014〉. 〈hal-01299732〉 Plus de détails...
The 3D global edge turbulence code TOKAM3X is used to study the properties of edge particle turbulent transport in circular limited plasmas, including both closed and open flux surfaces. Turbulence is driven by an incoming particle flux from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed. Simulations show the existence of a complex self-organization of turbulence transport coupling scales ranging from a few Larmor radii up to the machine scale. Particle transport is largely dominated by small scale turbulence with fluctuations forming quasi field-aligned filaments. Radial particle transport is intermittent and associated with the propagation of coherent structures on long distances via avalanches. Long range correlations are also found in the poloidal and toroidal direction. The statistical properties of fluctuations vary with the radial and poloidal directions, with larger fluctuation levels and intermittency found in the outboard scrape-off layer (SOL). Radial turbulent transport is strongly ballooned, with 90% of the flux at the separatrix flowing through the low-field side. One of the main consequences is the existence of quasi-sonic asymmetric parallel flows driving a net rotation of the plasma. Simulations also show the spontaneous onset of an intermittent E × B rotation characterized by a larger shear at the separatrix. Strong correlation is found between the turbulent particle flux and the E × B flow shear in a phenomenology reminiscent of H-mode physics. The poloidal position of the limiter is a key player in the observed dynamics.
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, IOP Publishing, 2015, 57 (5), pp.054014. 〈10.1088/0741-3335/57/5/054014〉. 〈hal-01299732〉
Richard Howard, Eric Serre. Large-eddy simulation in a mixing tee junction: High-order turbulent
statistics analysis. International Journal of Heat and Fluid Flow, Elsevier, 2015, 51, pp.65-77. 〈hal-01138803〉 Plus de détails...
This study analyses the mixing and thermal fluctuations induced in a mixing tee junction with circular cross-sections when cold water flowing in a pipe is joined by hot water from a branch pipe. This config- uration is representative of industrial piping systems in which temperature fluctuations in the fluid may cause thermal fatigue damage on the walls. Implicit large-eddy simulations (LES) are performed for equal inflow rates corresponding to a bulk Reynolds number Re= 39,080. Two different thermal boundary conditions are studied for the pipe walls; an insulating adiabatic boundary and a conducting steel wall boundary. The predicted flow structures show a satisfactory agreement with the literature. The velocity and thermal fields (including high-order statistics) are not affected by the heat transfer with the steel walls. However, predicted thermal fluctuations at the boundary are not the same between the flow and the solid, showing that solid thermal fluctuations cannot be predicted by the knowledge of the fluid thermal fluctuations alone. The analysis of high-order turbulent statistics provides a better understand- ing of the turbulence features. In particular, the budgets of the turbulent kinetic energy and temperature variance allows a comparative analysis of dissipation, production and transport terms. It is found that the turbulent transport term is an important term that acts to balance the production. We therefore use a priori tests to evaluate three different models for the triple correlation
Richard Howard, Eric Serre. Large-eddy simulation in a mixing tee junction: High-order turbulent
statistics analysis. International Journal of Heat and Fluid Flow, Elsevier, 2015, 51, pp.65-77. 〈hal-01138803〉
Journal: International Journal of Heat and Fluid Flow
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.420-423. 〈10.1016/j.jnucmat.2014.09.061〉. 〈hal-01225205〉 Plus de détails...
The influence of the plasma facing components material on the scrape-off layer plasma is investigated. In particular, the energy recycling is found to be more pronounced for tungsten wall compared with carbon wall. Edge plasma simulations performed with the transport code SOLEDGE2D-EIRENE show that this enhanced energy recycling in the tungsten case leads to an increase of the scrape-off layer temperature. Moreover, the energy recycling depends on the ion angle of incidence with the wall. A PIC code has been used to model the ion acceleration in the magnetic pre-sheath and determine the later angle of incidence. These simulations show that ions mostly impact the wall with rather shallow incident angles leading to a further increase of the energy recycling.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.420-423. 〈10.1016/j.jnucmat.2014.09.061〉. 〈hal-01225205〉
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, IOP Publishing, 2015, 55 (5), pp.053025. 〈hal-01225195〉 Plus de détails...
In the perspective of operating tungsten monoblocks in WEST, the ongoing major upgrade of the Tore Supra tokamak, a dedicated modelling effort has been carried out to simulate the interaction between the edge plasma and the tungsten wall. A new transport code, SolEdge2D–EIRENE, has been developed with the ability to simulate the plasma up to the first wall. This is especially important for steady state operation, where thermal loads on all the plasma facing components, even remote from the plasma, are of interest. Moreover, main chamber tungsten sources are thought to dominate the contamination of the plasma core. We present here in particular new developments aimed at improving the description of the interface between the plasma and the wall, namely a way to treat sheath physics in a more faithful way using the output of 1D particle in cell simulations. Moreover, different models for prompt redeposition have been implemented and are compared. The latter is shown to play an important role in the balance between divertor and main chamber sources.
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, IOP Publishing, 2015, 55 (5), pp.053025. 〈hal-01225195〉
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.654-658. 〈10.1016/j.jnucmat.2015.01.019〉. 〈hal-01225200〉 Plus de détails...
A 3D global turbulence fluid code, TOKAM3X is used to investigate the effect of the limiter position on the edge plasma parallel flows and density profiles. Six configurations with different poloidal contact points in the machine are considered. For each one, asymmetric quasi-sonic parallel flows are found, owing to the ballooning of radial turbulent transport around the LFS mid-plane. In spite of the relative simplicity of the model used (isothermal, sheat-limited, no recycling), simulations exhibit trends in-line with experimental findings. Reversal of the flows is found when the limiter is moved from −30° under to 30° above the outboard mid-plane. The SOL width varies with the poloidal location and depends notably on the poloidal position of the limiter. Turbulence itself is shown to be impacted by the position of the limiter, radial transport appearing less ballooned with a LFS limiter than with a HFS.
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.654-658. 〈10.1016/j.jnucmat.2015.01.019〉. 〈hal-01225200〉
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.489-492. 〈10.1016/j.jnucmat.2014.10.079〉. 〈hal-01225211〉 Plus de détails...
To understand the mechanisms behind poloidal asymmetries of the transport in the edge and SOL plasma, it is important to take into account drift velocity in the transport model. We investigate the effects of an imposed radial electric field on the plasma equilibrium in the transport code SOLEDGE2D. In the edge, we show an important modification of the flow pattern due to poloidal E × B drift velocity. The drift velocity generates asymmetry of the density through the Pfirsch–Schluter flows which creates an important parallel rotation through the viscous balance. In comparison to heat load imbalance studies in the SOL of divertor tokamak, a strong link between the amplitude of the radial electric field and the heat load imbalance in the SOL of limiter tokamak has been highlighted using different amplitude of the imposed radial electric field.
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, Elsevier, 2015, 463, pp.489-492. 〈10.1016/j.jnucmat.2014.10.079〉. 〈hal-01225211〉
H Guillard, M Bilanceri, C Colin, Philippe Ghendrih, G Giorgiani, et al.. Parallel Kelvin-Helmholtz instability in edge plasma. Journal of Physics: Conference Series, IOP Publishing, 2014, Joint Varenna-Lausanne International Workshop 2014, 561, pp.012009. 〈10.1088/1742-6596/561/1/012009〉. 〈hal-01100365〉 Plus de détails...
In the scrape-off layer (SOL) of tokamaks, the flow acceleration due to the presence of limiter or divertor plates rises the plasma velocity in a sonic regime. These high velocities imply the presence of a strong shear between the SOL and the core of the plasma that can possibly trigger some parallel shear flow instability. The existence of these instabilities, denoted as parallel Kelvin-Helmholtz instability in some works [1, 2] have been investigated theoretically in [3] using a minimal model of electrostatic turbulence composed of a mass density and parallel velocity equations. This work showed that the edge plasma around limiters might indeed be unstable to this type of parallel shear flow instabilities. In this work, we perform 3D simulations of the same simple mathematical model to validate an original finite volume numerical method aimed to the numerical study of edge plasma. This method combines the use of triangular unstructured meshes in the poloidal section and structured meshes in the toroidal direction and is particularly suited to the representation of the real complex geometry of the vacuum chamber of a tokamak. The numerical results confirm that in agreement with the theoretical expectations as well as with other numerical methods, the sheared flows in the SOL are subject to parallel Kelvin-Helmholtz instabilities. However, the growth rate of these instabilities is low and these computations require both a sufficient spatial resolution and a long simulation time. This makes the simulation of parallel Kelvin-Helmholtz instabilities a demanding benchmark.
H Guillard, M Bilanceri, C Colin, Philippe Ghendrih, G Giorgiani, et al.. Parallel Kelvin-Helmholtz instability in edge plasma. Journal of Physics: Conference Series, IOP Publishing, 2014, Joint Varenna-Lausanne International Workshop 2014, 561, pp.012009. 〈10.1088/1742-6596/561/1/012009〉. 〈hal-01100365〉
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak ă with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈10.1016/j.jcp.2014.05.025〉. 〈hal-01464707〉 Plus de détails...
To properly address turbulent transport in the edge plasma region of a ă tokamak, it is mandatory to describe the particle and heat outflow on ă wall components, using an accurate representation of the wall geometry. ă This is challenging for many plasma transport codes, which use a ă structured mesh with one coordinate aligned with magnetic surfaces. We ă propose here a penalization technique that allows modeling of particle ă and heat transport using such structured mesh, while also accounting for ă geometrically complex plasma-facing components. Solid obstacles are ă considered as particle and momentum sinks whereas ionic and electronic ă temperature gradients are imposed on both sides of the obstacles along ă the magnetic field direction using delta functions (Dirac). Solutions ă exhibit plasma velocities (M = 1) and temperatures fluxes at the ă plasma-wall boundaries that match with boundary conditions usually ă implemented in fluid codes. Grid convergence and error estimates are ă found to be in agreement with theoretical results obtained for neutral ă fluid conservation equations. The capability of the penalization ă technique is illustrated by introducing the non-collisional plasma ă region expected by the kinetic theory in the immediate vicinity of the ă interface, that is impossible when considering fluid boundary ă conditions. Axisymmetric numerical simulations show the efficiency of ă the method to investigate the large-scale transport at the plasma edge ă including the separatrix and in realistic complex geometries while ă keeping a simple structured grid. (C) 2014 Elsevier Inc. All rights ă reserved.
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak ă with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈10.1016/j.jcp.2014.05.025〉. 〈hal-01464707〉
Denis Martinand, Eric Serre, Richard M. Lueptow. Mechanisms for the transition to waviness for Taylor vortices. Physics of Fluids, American Institute of Physics, 2014, 26 (9), pp.094102. 〈10.1063/1.4895400〉. 〈hal-01300402〉 Plus de détails...
Building on the weakly nonlinear amplitude equation of the saturated Taylor vortices developing in a Taylor–Couette cell with a rotating inner cylinder and a fixed outer one, the physical mechanism underlying the destabilization of these vortices resulting in azimuthal waviness is addressed using Floquet analysis. For narrow gap configurations, analysis and direct numerical simulations together with existing experimental results support the idea that the waviness is generated by the axial shear in the azimuthal velocity due to the alternate advection by the Taylor vortices of azimuthal momentum between the cylinders. For wide gap configurations, this mechanism is no longer able to drive the azimuthal waviness and a different mechanism tends to select a subharmonic instability.
Denis Martinand, Eric Serre, Richard M. Lueptow. Mechanisms for the transition to waviness for Taylor vortices. Physics of Fluids, American Institute of Physics, 2014, 26 (9), pp.094102. 〈10.1063/1.4895400〉. 〈hal-01300402〉
Jose Joaquin Sanchez-Alvarez, Eric Serre, Emilia Arco, Friedrich.H Busse. Geometry effects on Rayleigh-Benard convection in rotating annular ă layers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89 (6), 〈10.1103/PhysRevE.89.063013〉. 〈hal-01464703〉 Plus de détails...
Rayleigh-Benard convection is investigated in rotating annular cavities ă at a moderate dimensionless rotation rate Omega = 60. The onset of ă convection is in the form of azimuthal traveling waves that set in at ă the sidewalls and at values of the Rayleigh number significantly below ă the value of the onset of convection in an infinitely extended layer. ă The present study addresses the effects of curvature and confinement on ă the onset of sidewall convection by using three-dimensional spectral ă solutions of the Oberbeck-Boussinesq equations. Such solutions ă demonstrate that the curvature of the outer boundary promotes the onset ă of the wall mode, while the opposite curvature of the inner boundary ă tends to delay the onset of the wall mode. An inner sidewall with a ă radius as low as one tenth of its height is sufficient, however, to ă support the onset of a sidewall mode. When radial confinement is ă increased the two independent traveling waves interact and eventually ă merge to form a nearly steady pattern of convection.
Jose Joaquin Sanchez-Alvarez, Eric Serre, Emilia Arco, Friedrich.H Busse. Geometry effects on Rayleigh-Benard convection in rotating annular ă layers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89 (6), 〈10.1103/PhysRevE.89.063013〉. 〈hal-01464703〉
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Alejandro Paredes, Eric Serre, Frédéric Schwander, Philippe Ghendrih, Patrick Tamain. Numerical fluid modelling of the plasma edge response to a 3D object and application to mach probe measurements. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.373-377. 〈10.1002/ctpp.201410028〉. 〈hal-01050666〉 Plus de détails...
The penalization method is used to model the interaction of 3D probe with an isothermal plasma. Density maps show that the region perturbed by the obstacle, is not restricted to its near neighbourhood, but can extend to the whole SOL. In the particular case of a probe, which is used to measure local plasma parameters, this impact can lead to violation of assumptions of locality of the perturbation usually used in determining Mach number from the imbalance in density on both sides of the probe.
Alejandro Paredes, Eric Serre, Frédéric Schwander, Philippe Ghendrih, Patrick Tamain. Numerical fluid modelling of the plasma edge response to a 3D object and application to mach probe measurements. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.373-377. 〈10.1002/ctpp.201410028〉. 〈hal-01050666〉
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich Busse. Geometry effects on the onset of rotating Rayleigh-Bénard convection in annuli. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89, pp.063013. 〈hal-01087216〉 Plus de détails...
Rayleigh-Bénard convection is investigated in rotating annular cavities at a moderate rotationrate (square root of the Taylor number) Omega= 60. The onset of convection is in the form of azimuthaltraveling waves that set in at the sidewalls and at values of the Rayleigh number significantly belowthe value of the onset of convection in an infinitely extended layer. When curvature effect becomessignificant, the waves traveling along the sidewalls have different critical Rayleigh numbers and com-plex Guinzburg-Landau equations are no longer applicable. The present study addresses the effectsof curvature and confinement on the onset of sidewall convection by using three-dimensional spectralsolutions of the Oberbeck-Boussinesq equations. Such solutions demonstrate that the curvature ofthe outer boundary promotes the onset of the wall mode, while the opposite curvature of the innerboundary tends to delay the onset of the wall mode. When radial confinement is increased the twoindependent traveling waves can interact and eventually merge to form a nearly steady pattern ofconvection.
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich Busse. Geometry effects on the onset of rotating Rayleigh-Bénard convection in annuli. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 2014, 89, pp.063013. 〈hal-01087216〉
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Guillaume Fontaine, Sébastien Poncet, Eric Serre. Multidomain Extension of a Pseudospectral Algorithm for the Direct Simulation of Wall-Confined Rotating Flows. M. Azaiez, H. El Fekih, J.S. Hesthaven. Lecture Notes in Computational Science and Engineering, 95, Springer, pp.261 - 271, 2014, 〈10.1007/978-3-319-01601-6_21〉. 〈hal-01098589〉 Plus de détails...
In this work, we improve an existing pseudospectral algorithm, in order to extend its properties to a multidomain patching of a rotating cavity. Viscous rotating flows have been widely studied over the last decades, either on industrial or aca-demic approaches. Nevertheless, the range of Reynolds numbers reached in indus-trial devices implies very high resolutions of the spatial problem, which are clearly unreachable using a monodomain approach. Hence, we worked on the multido-main extension of the existing divergence-free Navier-Stokes solver with a Schur approach. The particularity of such an approach is that it does not require any sub-domain superposition: the value of a variable on the boundary between two adjacent subdomains is treated as a boundary condition of a local Helmholtz solver. This value is computed on a direct way via a so-called continuity influence matrix and the derivative jump of an homogeneous solution computed independently on each subdomain. Such a method is known to have both good scalability and accuracy. It has been validated on two well documented three-dimensional rotating flows.
Guillaume Fontaine, Sébastien Poncet, Eric Serre. Multidomain Extension of a Pseudospectral Algorithm for the Direct Simulation of Wall-Confined Rotating Flows. M. Azaiez, H. El Fekih, J.S. Hesthaven. Lecture Notes in Computational Science and Engineering, 95, Springer, pp.261 - 271, 2014, 〈10.1007/978-3-319-01601-6_21〉. 〈hal-01098589〉
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.432-436. 〈10.1002/ctpp.201410018〉. 〈hal-01050505〉 Plus de détails...
We present numerical simulations of plasma transport obtained with the SOLEDGE2D code coupled to the EIRENE Montecarlo code for neutrals. We consider a double null magnetic configuration in a WEST geometry. Density and temperatures parallel profiles in the SOL domain are presented as well as Mach profile. We detail how using the penalization technique we are able to model plasma transport up to the first wall having access to energy and particle fluxes on the entire chamber wall. Moreover, we present the computed 2D contour map of the plasma mach number and of the magnitude of the ionisation source term in the whole poloidal section, emphasizing how complex and realistic geometries can be handled thanks to the penalization technique.
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.432-436. 〈10.1002/ctpp.201410018〉. 〈hal-01050505〉
Nils Tilton, Eric Serre, Denis Martinand, Richard M. Lueptow. A 3D pseudospectral algorithm for fluid flows with permeable walls. Application to filtration. Computers and Fluids, Elsevier, 2014, 93, pp.129-145. 〈10.1016/j.compfluid.2014.01.003〉. 〈hal-01053339〉 Plus de détails...
The present work proposes a Chebyshev-collocation Fourier-Galerkin pseudospectral method for simulating unsteady, three-dimensional, fluid flows in cylindrical geometries with pressure-driven flow through permeable boundaries. Such systems occur in diverse applications and are challenging to simulate due to an additional velocity-pressure coupling on the permeable walls through Darcy's law. The present work extends the projection method of Raspo et al. (2002) to assure Darcy's law is satisfied exactly. A multidomain solver allows the efficient treatment of open boundary conditions that necessitate permeability buffers and a sponge layer. The method is spectrally convergent, and we demonstrate that pressure-prediction is necessary to obtain second-order temporal accuracy. The ability of the method to simulate complicated physical systems is demonstrated by simulating subcritical and supercritical flows in rotating filtration in Taylor-Couette cells. For subcritical cases, numerical results show excellent agreement with analytical solutions. For supercritical cases, the numerical method accurately resolves convectively and absolutely unstable flows with traveling toroidal and helical vortical structures that are in good agreement with a local linear stability analysis and experimental observations.
Nils Tilton, Eric Serre, Denis Martinand, Richard M. Lueptow. A 3D pseudospectral algorithm for fluid flows with permeable walls. Application to filtration. Computers and Fluids, Elsevier, 2014, 93, pp.129-145. 〈10.1016/j.compfluid.2014.01.003〉. 〈hal-01053339〉
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.555-559. 〈10.1002/ctpp.201410017〉. 〈hal-01053290〉 Plus de détails...
The 3D fluid turbulence code TOKAM3X is used to investigate the 3D properties of edge turbulent transport and their impact on poloidal asymmetries. Simulations are run in circular limited plasmas in a domain covering both closed and open flux surfaces. Turbulence characteristics exhibit large inhomogeneities both in the radial and poloidal directions reminiscent of experimental observations. The low field side mid-plane in particular is found to be locally more fluctuating and intermittent than the rest of the Scrape-Off-Layer (SOL). As a consequence of this asymmetry, radial turbulent transport, that represents 80 to 90% of the total radial flux, is strongly ballooned, with 75% of the flux flowing through LFS. The equilibrium of the edge plasma is impacted by this asymmetry through the existence of large amplitude asymmetric parallel flows as well as through the development of poloidally asymmetric radial decay lengths making it impossible to define a single SOL width.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.555-559. 〈10.1002/ctpp.201410017〉. 〈hal-01053290〉
Clothilde Colin, Patrick Tamain, Philippe Ghendrih, Frederic Schwander, Eric Serre. Impact of a Langmuir probe on turbulence measurements in the Scrape-Off-Layer of tokamaks. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.543-548. 〈10.1002/ctpp.201410087〉. 〈hal-01019696〉 Plus de détails...
An issue for Langmuir probe measurements of SOL turbulence concerns the impact of the probe itself on plasma transport. The aim of this paper is to investigate this issue with a synthetic reconstruction of Langmuir probe measurements by inserting a synthetic probe into a 2D fluid SOL turbulence code. The effect of a biased probe is analysed as a function of its size. It is shown that the probe creates a transport barrier whose effect is non-local and affects the current's circulation in the plasma. The plasma density is depleted by the presence of the probe as well as the electrostatic potential. A strong impact on turbulence can also be observed. Such observations imply that the probed turbulence can differ significantly from the probe-free turbulence
Clothilde Colin, Patrick Tamain, Philippe Ghendrih, Frederic Schwander, Eric Serre. Impact of a Langmuir probe on turbulence measurements in the Scrape-Off-Layer of tokamaks. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.543-548. 〈10.1002/ctpp.201410087〉. 〈hal-01019696〉
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (122001), 〈10.1088/0741-3335/56/12/122001〉. 〈hal-01225185〉 Plus de détails...
We present a comprehensive picture of the mechanisms driving the transition from subsonic to supersonic flows in tokamak plasmas. We demonstrate that supersonic parallel flows into the divertor volume are ubiquitous at low density and governed by the divertor magnetic geometry. As the density is increased, subsonic divertor plasmas are recovered. On detachment, we show the change in particle source can also drive the transition to a supersonic regime. The comprehensive theoretical analysis is completed by simulations in ITER geometry. Such results are essential in assessing the divertor performance and when interpreting measurements and experimental evidence. The generation of large-scale flows in laboratory plasma is a highly non-linear problem. In a standard fashion it is considered that the flows remain subsonic away from the wall, the occurrence of supersonic flows being singular. We show here that the geometrical features of key configurations for fusion plasma can lead to supersonic flows.
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (122001), 〈10.1088/0741-3335/56/12/122001〉. 〈hal-01225185〉
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.378-382. 〈10.1002/ctpp.201410026〉. 〈hal-01053281〉 Plus de détails...
To support ITER divertor design, the WEST project on Tore Supra aims at studying high heat fluxes on tungsten monoblock during long pulses. In that persective, a particular attention is paid to simulate the edge plasma interaction with complex PFCs using the transport code SOLEDGE2D-EIRENE. The plasma response to a heating and puffing scenario is described as well as the so-called divertor density regimes, characterizing the operational domain of the WEST divertor. These results are compared for two different magnetic configurations: a semi-open double null divertor with the X-point away from the target plates and a shallow divertor configuration with the X-point close to the targets.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, Wiley-VCH Verlag, 2014, 54 (4-6), pp.378-382. 〈10.1002/ctpp.201410026〉. 〈hal-01053281〉
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈hal-01087225〉 Plus de détails...
To properly address turbulent transport in the edge plasma region of a tokamak, it is mandatory to describe the particle and heat outflow on wall components, using an accurate representation of the wall geometry. This is challenging for many plasma transport codes, which use a structured mesh with one coordinate aligned with magnetic surfaces. We propose here a penalization technique that allows modelingof particle and heat transport using such structured mesh, while also accounting for geometrically complex plasma-facing components. Solid obstacles are considered as particle and momentum sinks whereas ionic and electronic temperature gradients are imposed on both sides of the obstacles along the magnetic field direction using delta functions (Dirac). Solutions exhibit plasma velocities (M=1) and temperatures fluxes at the plasma–wall boundaries that match with boundary conditions usually implemented in fluid codes. Grid convergence and error estimates are found to be in agreement with theoretical results obtained for neutral fluid conservation equations. The capability of the penalization technique is illustrated by introducing the non-collisional plasma region expected by the kinetic theory in the immediate vicinity of the interface, that is impossible when considering fluid boundary conditions. Axisymmetric numerical simulations show the efficiency of the method to investigate the large-scale transport at the plasma edge including the separatrix and in realistic complex geometries while keeping a simple structured grid.
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, Elsevier, 2014, 274, pp.283-298. 〈hal-01087225〉
Philippe Ghendrih, Thomas Auphan, B. Bensiali, Marco Bilanceri, K. Bodi, et al.. Divertor imbalance and divertor density regimes for ballooned cross-field turbulence. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.S368-S371. 〈http://www.sciencedirect.com/science/article/pii/S0022311513000780〉. 〈10.1016/j.jnucmat.2013.01.070〉. 〈hal-00920748〉 Plus de détails...
The ballooned nature of cross-field transport is shown to govern the steady state divertor imbalance of the energy flux leading to a factor 10 between the low field side and high field energy flux. An even stronger ratio is found for the divertor temperatures. Conversely the particle flux is expected to be a factor 10 larger on the high field side than on the low field side. The transition to detachment, close to divertor thermal collapse, exhibits several constraints to maintain steady state solutions. These constraints, related in particular to a large drop of the divertor density upon detachment, are shown to strongly correlate the pressure and particle flux variation along the field line and consequently the various loss channels. This delicate balance between different mechanisms is a possible understanding of the difficulty reported in detached plasma operation and simulation.
Philippe Ghendrih, Thomas Auphan, B. Bensiali, Marco Bilanceri, K. Bodi, et al.. Divertor imbalance and divertor density regimes for ballooned cross-field turbulence. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.S368-S371. 〈http://www.sciencedirect.com/science/article/pii/S0022311513000780〉. 〈10.1016/j.jnucmat.2013.01.070〉. 〈hal-00920748〉
Eric Serre, Mathieu Minguez, R. Pasquetti, Emmanuel Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a french-german collaborative evaluation of LES and DES. Computers and Fluids, Elsevier, 2013, 78, pp.10-23. 〈ujm-00860576〉 Plus de détails...
The paper presents a comparative analysis of recent simulations, conducted in the framework of a French-German collaboration on LES of Complex Flows, for the so-called Ahmed body at Reynolds number 768000 and slant angle 25°. It provides a juxtaposition of results obtained with different eddy-resolving modeling approaches, i.e. two Large Eddy Simulations (LES) on body-fitted curvilinear grids, a stabilized spectral method and a Detachted Eddy Simulation (DES) on an unstructured grid. The paper presents a comprehensive data base including both instantaneous and statistical data. A central achievement is the comparative assessment of the different approaches with an appreciation of the respective advantages and disadvantages of the various methods. In particular, issues on computational cost and ease of implementation are addressed in addition to the quality of results.
Eric Serre, Mathieu Minguez, R. Pasquetti, Emmanuel Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a french-german collaborative evaluation of LES and DES. Computers and Fluids, Elsevier, 2013, 78, pp.10-23. 〈ujm-00860576〉
Hugo Bufferand, B. Bensiali, J. Bucalossi, G. Ciraolo, P. Genesio, et al.. Near wall plasma simulation using penalization technique with the transport code Soledge2D-EIRENE. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.445-448. 〈10.1016/j.jnucmat.2013.01.090〉. 〈hal-01101345〉 Plus de détails...
In order to model plasma interaction with full complexity of the geometry of PFCs, an immersed method to impose boundary conditions has been implemented in the transport code SolEdge2D. This penalization technique has proven to properly recover Bohm boundary conditions, including supersonic solutions at the sheath entrance. The role of the ionization source has been taken into account by coupling SolEdge2D with the 3D kinetic neutral code Eirene. Density regimes are properly recovered and major differences between core located and divertor located ionization source regimes are emphasized. One also presents main chamber wall recycling regime simulations that can now be addressed with simulations of the entire edge plasma up to the wall.
Hugo Bufferand, B. Bensiali, J. Bucalossi, G. Ciraolo, P. Genesio, et al.. Near wall plasma simulation using penalization technique with the transport code Soledge2D-EIRENE. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.445-448. 〈10.1016/j.jnucmat.2013.01.090〉. 〈hal-01101345〉
A. Paredes, Hugo Bufferand, F. Schwander, G. Ciraolo, E. Serre, et al.. Penalization technique to model wall-component impact on heat and mass transport in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.625-628. 〈10.1016/j.jnucmat.2013.01.131〉. 〈hal-01101342〉 Plus de détails...
The original and computationally efficient volume penalization technique Ref. [1], proposed for an isothermal plasma to recover the Bohm boundary condition at the plasma–obstacle interface, is extended to model 3D obstacles. It is then generalized to handle electron and ion temperatures in a 1D model. Results in 3D simulations show that the geometry of secondary limiter has an influence on the density and particle flux profiles, breaking its toroidal symmetry and introducing profile gaps of magnitude of 20%. On the other hand, the generalization of the penalization scheme to the non-isothermal case demands to deal with new Neumann conditions on the heat fluxes. Those boundary conditions require the introduction of new mask functions to ensure that the Bohm boundary condition remains satisfied.
A. Paredes, Hugo Bufferand, F. Schwander, G. Ciraolo, E. Serre, et al.. Penalization technique to model wall-component impact on heat and mass transport in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2013, 438, pp.625-628. 〈10.1016/j.jnucmat.2013.01.131〉. 〈hal-01101342〉
Bontoux P., Serre E.. Special Issue LES of Turbulence Aeroacoustics and Combustion. 78, pp.V-V, 2013, 〈10.1016/S0045-7930(13)00141-2〉. 〈hal-01313529〉 Plus de détails...
Eric Serre, M. Minguez, R. Pasquetti, E. Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a French-German collaborative evaluation of LES and DES. Computers and Fluids, Elsevier, 2013, 78, pp.10-23. 〈10.1016/j.compfluid.2011.05.017〉. 〈hal-01101350〉 Plus de détails...
The paper presents a comparative analysis of recent simulations, conducted in the framework of a French-German collaboration on LES of Complex Flows, for the so-called Ahmed body at Reynolds number 768000 and slant angle 25°. It provides a juxtaposition of results obtained with different eddy-resolving modeling approaches, i.e. two Large Eddy Simulations (LES) on body-fitted curvilinear grids, a stabilized spectral method and a Detachted Eddy Simulation (DES) on an unstructured grid. The paper presents a comprehensive data base including both instantaneous and statistical data. A central achievement is the comparative assessment of the different approaches with an appreciation of the respective advantages and disadvantages of the various methods. In particular, issues on computational cost and ease of implementation are addressed in addition to the quality of results.
Eric Serre, M. Minguez, R. Pasquetti, E. Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a French-German collaborative evaluation of LES and DES. Computers and Fluids, Elsevier, 2013, 78, pp.10-23. 〈10.1016/j.compfluid.2011.05.017〉. 〈hal-01101350〉
Noele Peres, Sébastien Poncet, Eric Serre. A 3D pseudospectral method for cylindrical coordinates. Application to the simulations of rotating cavity flows. Journal of Computational Physics, Elsevier, 2012, 231, pp.6290-6305. 〈10.1016/j.jcp.2012.04.033〉. 〈hal-00822026〉 Plus de détails...
The present work proposes a collocation spectral method for solving the three-dimensional Navier-Stokes equations using cylindrical coordinates. The whole diameter -R < r < R is discretized with an even number of radial Gauss-Lobatto collocation points and an angular shift is introduced in the Fourier transform that avoid pole and parity conditions usually required. The method keeps the spectral convergence that reduces the number of grid points with respect to lower-order numerical methods. The grid-points distribution densifies the mesh only near the boundaries that makes the algorithm well-suited to simulate rotating cavity flows where thin layers develop along the walls. Comparisons with reliable experimental and numerical results of the literature show good quantitative agreements for flows driven by rotating discs in tall cylinders and thin inter-disc cavities. Associated to a spectral vanishing viscosity [E. Séverac, E. Serre, A spectral vanishing viscosity for the LES of turbulent flows within rotating cavities, J. Comp. Phys. 226 (2007) 1234-1255], the method provides very promising LES results of turbulent cavity flows.
Noele Peres, Sébastien Poncet, Eric Serre. A 3D pseudospectral method for cylindrical coordinates. Application to the simulations of rotating cavity flows. Journal of Computational Physics, Elsevier, 2012, 231, pp.6290-6305. 〈10.1016/j.jcp.2012.04.033〉. 〈hal-00822026〉
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Incorporating Darcy's law for pure solvent flow through porous tubes: Asymptotic solution and numerical simulations. AIChE Journal, Wiley, 2012, 58 (7), pp.2030-2044. 〈10.1002/aic.13823〉. 〈hal-01032148〉 Plus de détails...
A generalized solution for pressure-driven, incompressible, Newtonian flow in a porous tubular membrane is challenging due to the coupling between the transmembrane pressure and velocity. To date, all analytical solutions require simplifications such as neglecting the coupling between the transmembrane pressure and velocity, assuming the form of the velocity fields, or expanding in powers of parameters involving the tube length. Moreover, previous solutions have not been validated with comparison to direct numerical simulation (DNS). We comprehensively revisit the problem to present a robust analytical solution incorporating Darcy's law on the membrane. We make no assumptions about the tube length or form of the velocity fields. The analytic solution is validated with detailed comparison to DNSs, including cases of axial flow exhaustion and cross flow reversal. We explore the validity of typical assumptions used in modeling porous tube flow and present a solution for porous channels in Supporting Information.
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Incorporating Darcy's law for pure solvent flow through porous tubes: Asymptotic solution and numerical simulations. AIChE Journal, Wiley, 2012, 58 (7), pp.2030-2044. 〈10.1002/aic.13823〉. 〈hal-01032148〉
Rodriguez S., Viaud B., Serre E.. Novel outflow boundary conditions for spectral direct numerical simulation of open rotating flows. Lectures notes in comp. Sc. and Eng., 95, Springer, pp.383--392, 2012, 978-3-319-01601-6. 〈hal-01313535〉 Plus de détails...
Rodriguez S., Viaud B., Serre E.. Novel outflow boundary conditions for spectral direct numerical simulation of open rotating flows. Lectures notes in comp. Sc. and Eng., 95, Springer, pp.383--392, 2012, 978-3-319-01601-6. 〈hal-01313535〉
Fontaine G., Poncet S., Serre E.. Multidomain extension of a divergence free pseudo-spectral algorithm for the DNS of wall-confined rotating flows. Lectures notes in comp. Sc. and Eng., 95, Springer, pp.261--271, 2012, 978-3-319-01601-6. 〈hal-01313536〉 Plus de détails...
Fontaine G., Poncet S., Serre E.. Multidomain extension of a divergence free pseudo-spectral algorithm for the DNS of wall-confined rotating flows. Lectures notes in comp. Sc. and Eng., 95, Springer, pp.261--271, 2012, 978-3-319-01601-6. 〈hal-01313536〉
Ouafa Bouloumou, Eric Serre, Patrick Bontoux, J. Fröhlich. A 3D pseudo-spectral low Mach-number solver for buoyancy driven flows with large temperature differences. Computers and Fluids, Elsevier, 2012, 66, pp.107-120. 〈10.1016/j.compfluid.2012.05.014〉. 〈hal-00834130〉 Plus de détails...
A three-dimensional spectral method based on a Chebyshev/Chebyshev/Fourier discretization is proposed to integrate the Navier-Stokes equations for natural convection flow with large temperature differences under the low Mach-number approximation. The generalized Stokes problem arising from the time discretization by a second-order semi-implicit scheme is solved by a preconditioned iterative Uzawa algorithm. The spectrally convergent algorithm is validated on well-documented Boussinesq and non-Boussinesq benchmarks. Finally, non-Boussineq convection is investigated in a tall differentially heated cavity of aspect ratio 8 with one homogeneous direction. The technique is shown to be efficient in terms of computing performances and accuracy. The study brings new stability results evidencing 3D effects compared to both Boussinesq convection and former two-dimensional non-Boussinesq solutions. In particular, for Ra ⩾ 105 two-dimensional solutions are shown to be unstable with respect to three-dimensional perturbations. A Görtler-type instability grows in the region of the curved streamlines at both ends of the cavity and gives rise to 3D steady and oscillatory solutions. At higher Rayleigh numbers, these vortices eventually interact with a boundary layer instability leading to complex dynamics with multiple steady and unsteady stable solutions.
Ouafa Bouloumou, Eric Serre, Patrick Bontoux, J. Fröhlich. A 3D pseudo-spectral low Mach-number solver for buoyancy driven flows with large temperature differences. Computers and Fluids, Elsevier, 2012, 66, pp.107-120. 〈10.1016/j.compfluid.2012.05.014〉. 〈hal-00834130〉
Philippe Meliga, Gregory Pujals, Eric Serre. Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability. Physics of Fluids, American Institute of Physics, 2012, 24, pp.061701. 〈10.1063/1.4724211〉. 〈hal-01061797〉 Plus de détails...
We use adjoint-based gradients to analyze the sensitivity of turbulent wake past a D-shaped cylinder at Re = 13000. We assess the ability of a much smaller control cylinder in altering the shedding frequency, as predicted by the eigenfrequency of the most unstable global mode to the mean flow. This allows performing beforehand identification of the sensitive regions, i.e., without computing the actually controlled states. Our results obtained in the frame of 2-D, unsteady Reynolds-averaged Navier-Stokes compare favorably with experimental data reported by Parezanović and Cadot [J. Fluid Mech.693, 115 (2012)] and suggest that the control cylinder acts primarily through a local modification of the mean flow profiles.
Philippe Meliga, Gregory Pujals, Eric Serre. Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability. Physics of Fluids, American Institute of Physics, 2012, 24, pp.061701. 〈10.1063/1.4724211〉. 〈hal-01061797〉
Eric Serre, Hugo Bufferand, A. Paredes, Frédéric Schwander, Guido Ciraolo, et al.. Numerical modeling of the impact of geometry and wall components on transport in the tokamak edge. Contributions to Plasma Physics, Wiley-VCH Verlag, 2012, 52 (5-6), pp.401-405. 〈10.1002/ctpp.201210023〉. 〈hal-00848473〉 Plus de détails...
Eric Serre, Hugo Bufferand, A. Paredes, Frédéric Schwander, Guido Ciraolo, et al.. Numerical modeling of the impact of geometry and wall components on transport in the tokamak edge. Contributions to Plasma Physics, Wiley-VCH Verlag, 2012, 52 (5-6), pp.401-405. 〈10.1002/ctpp.201210023〉. 〈hal-00848473〉
M. Minguez, Christophe Brun, R. Pasquetti, E. Serre. Experimental and high-order LES analysis of the flow in near-wall region of a square cylinder. International Journal of Heat and Fluid Flow, Elsevier, 2011, 32 (3), pp.558-566. 〈10.1016/j.ijheatfluidflow.2011.03.009〉. 〈hal-01299962〉 Plus de détails...
A coupled experimental/numerical analysis of turbulent flow past a square cylinder is performed at the ERCOFTAC Reynolds number Re = U∞D/ν = 21,400, where U∞ is the inflow velocity and D the cylinder height. Complementary Laser Doppler Velocimetry (LDV) and high-order large-eddy simulations (LES) approaches, based on a spectral vanishing technique (SVV-LES), provide a comprehensive data base including both instantaneous data and post-processed statistics. Beyond these results, an achievement of the paper is to investigate the coherent structures developing on the sides and in the wake of the cylinder with a special focus on the flow features in the near-wall region. The flow is found to separate at the leading edge of the cylinder with the occurence of three-dimensional Kelvin–Helmholtz (KH) pairings localized in the separating shear layer. The interaction between these KH vortical structures and Von Kármán vortex shedding (VK) in the near wake is discussed based on both visualisations and frequency analysis. In particular, signatures of VK and KH vortical structures are found on velocity time samples.
M. Minguez, Christophe Brun, R. Pasquetti, E. Serre. Experimental and high-order LES analysis of the flow in near-wall region of a square cylinder. International Journal of Heat and Fluid Flow, Elsevier, 2011, 32 (3), pp.558-566. 〈10.1016/j.ijheatfluidflow.2011.03.009〉. 〈hal-01299962〉
Journal: International Journal of Heat and Fluid Flow
Stéphane Viazzo, Sébastien Poncet, Eric Serre, Anthony Randriamampianina, Patrick Bontoux. High-order Large Eddy Simulations of Confined Rotor-Stator Flows. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2011, 88, pp.63-75. 〈10.1007/s10494-011-9345-0〉. 〈hal-00678841〉 Plus de détails...
In many engineering and industrial applications, the investigation of rotating turbulent flow is of great interest. In rotor-stator cavities, the centrifugal and Coriolis forces have a strong influence on the turbulence by producing a secondary flow in the meridian plane composed of two thin boundary layers along the disks separated by a non-viscous geostrophic core. Most numerical simulations have been performed using RANS and URANS modelling, and very few investigations have been performed using LES. This paper reports on quantitative comparisons of two high-order LES methods to predict a turbulent rotor-stator flow at the rotational Reynolds number Re=400000. The classical dynamic Smagorinsky model for the subgrid-scale stress (Germano et al., Phys Fluids A 3(7):1760-1765, 1991) is compared to a spectral vanishing viscosity technique (Séverac & Serre, J Comp Phys 226(2):1234-1255, 2007). Numerical results include both instantaneous data and postprocessed statistics. The results show that both LES methods are able to accurately describe the unsteady flow structures and to satisfactorily predict mean velocities as well as Reynolds stress tensor components. A slight advantage is given to the spectral SVV approach in terms of accuracy and CPU cost. The strong improvements obtained in the present results with respect to RANS results confirm that LES is the appropriate level of modelling for flows in which fully turbulent and transition regimes are involved.
Stéphane Viazzo, Sébastien Poncet, Eric Serre, Anthony Randriamampianina, Patrick Bontoux. High-order Large Eddy Simulations of Confined Rotor-Stator Flows. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2011, 88, pp.63-75. 〈10.1007/s10494-011-9345-0〉. 〈hal-00678841〉
Stéphane Viazzo, Sébastien Poncet, Eric Serre, Anthony Randriamampianina, Patrick Bontoux. High-order Large Eddy Simulations of Confined Rotor-Stator Flows. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2011, 88, pp.63-75. 〈10.1007/s10494-011-9345-0〉. 〈hal-00822030〉 Plus de détails...
In many engineering and industrial applications, the investigation of rotating turbulent flow is of great interest. In rotor-stator cavities, the centrifugal and Coriolis forces have a strong influence on the turbulence by producing a secondary flow in the meridian plane composed of two thin boundary layers along the disks separated by a non-viscous geostrophic core. Most numerical simulations have been performed using RANS and URANS modelling, and very few investigations have been performed using LES. This paper reports on quantitative comparisons of two high-order LES methods to predict a turbulent rotor-stator flow at the rotational Reynolds number Re=400000. The classical dynamic Smagorinsky model for the subgrid-scale stress (Germano et al., Phys Fluids A 3(7):1760-1765, 1991) is compared to a spectral vanishing viscosity technique (Séverac & Serre, J Comp Phys 226(2):1234-1255, 2007). Numerical results include both instantaneous data and postprocessed statistics. The results show that both LES methods are able to accurately describe the unsteady flow structures and to satisfactorily predict mean velocities as well as Reynolds stress tensor components. A slight advantage is given to the spectral SVV approach in terms of accuracy and CPU cost. The strong improvements obtained in the present results with respect to RANS results confirm that LES is the appropriate level of modelling for flows in which fully turbulent and transition regimes are involved.
Stéphane Viazzo, Sébastien Poncet, Eric Serre, Anthony Randriamampianina, Patrick Bontoux. High-order Large Eddy Simulations of Confined Rotor-Stator Flows. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2011, 88, pp.63-75. 〈10.1007/s10494-011-9345-0〉. 〈hal-00822030〉
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S574-S578. 〈10.1016/j.jnucmat.2010.12.318〉. 〈hal-00848528〉 Plus de détails...
We are interested here in modelling the electron and ion temperature fields, Te and Ti respectively, in order to understand the main trends that govern the ratio Ti/Te that is being better documented in the SOL with RFA probes and . The experimental evidence gathered from several devices indicates that this temperature ratio significantly exceeds unity in most data sets that have been analysed, including measurements in the SOL of limiter devices like Tore Supra. Several issues of interest have been addressed with this version of the SOLEDGE-2D code. First, we have analysed the width of the SOL heat channels to the wall components and compared these values to analytical expressions. The key control mechanism of the width of the SOL heat channel is given by a balance between the sheath boundary conditions and the transverse transport. More advanced simulations address the interplay between the edge and SOL plasma allowing one to recover regimes with Ti/Te > 1.
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S574-S578. 〈10.1016/j.jnucmat.2010.12.318〉. 〈hal-00848528〉
Guillaume Chiavassa, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Hervé Guillard, et al.. Parallel expansion of density bursts. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S613-S616. 〈10.1016/j.jnucmat.2010.10.086〉. 〈hal-00848522〉 Plus de détails...
Evidence of poloidally localized cross-field transport in experiments and theoretical analysis of turbulence transport governs the onset of parallel transport towards equilibrium. When cross-field transport appears in bursts, both for ELM relaxation events and microturbulence, the parallel transport of particles is shown to generate fronts that propagate with supersonic velocities. It is shown that after a short transient the density structure is no longer monotonic and that the two fronts (one co, the other counter the magnetic field) are independent. Furthermore, the time trace of the particle flux at a given location is characterized by a sharp rise followed by a longer time scale relaxation. Comparing the time delay and magnitude of the density burst at two locations allows to estimate the magnitude and the location of the generation of the front.
Guillaume Chiavassa, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Hervé Guillard, et al.. Parallel expansion of density bursts. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S613-S616. 〈10.1016/j.jnucmat.2010.10.086〉. 〈hal-00848522〉
Hugo Bufferand, Guido Ciraolo, Livia Isoardi, Guillaume Chiavassa, Frédéric Schwander, et al.. Applications of SOLEDGE-2D code to complex SOL configurations and analysis of Mach probe measurements. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S589-S592. 〈10.1016/j.jnucmat.2010.11.037〉. 〈hal-00848483〉 Plus de détails...
A series of experiments dedicated to the determination of the ballooning nature of the edge and SOL transport has been achieved on Tore Supra and , proposing a quantitative characterization of the radial flux that enters the SOL. The aim of this paper is to back up the interpretation of these probe flow measurements making use of SOLEDGE-2D code. In particular, this fluid code allows one to study density and parallel momentum transport in a 2D geometry including edge and SOL region. Moreover, thanks to an appropriate numerical technique recently proposed and , SOLEDGE-2D code is also able to deal with a complex geometry of plasma facing components including main and secondary limiters.
Hugo Bufferand, Guido Ciraolo, Livia Isoardi, Guillaume Chiavassa, Frédéric Schwander, et al.. Applications of SOLEDGE-2D code to complex SOL configurations and analysis of Mach probe measurements. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S589-S592. 〈10.1016/j.jnucmat.2010.11.037〉. 〈hal-00848483〉
Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S601-S604. 〈10.1016/j.jnucmat.2010.10.073〉. 〈hal-00848536〉 Plus de détails...
The transition between the core and scrape-off layer of a tokamak corresponds to a marked momentum shear layer, owing to sheath acceleration on limiters which drives near-sonic flows along the plasma magnetic field in the scrape-off layer, and a parallel shear flow instability can possibly be triggered. The possibility of this instability driven by the velocity gradient is investigated numerically, using a minimum model of particle and parallel momentum transport in the edge of a tokamak, in a computational domain modelling a limiter plasma with background turbulence modelled as an effective diffusion. It is found that unstable regions can exist in the vicinity of a limiter, in agreement with experimental findings, when momentum radial transport - and therefore coupling between SOL and core flows - is sufficiently weak. Instability is reinforced by core rotation, and is found to be maximum downstream of the limiter (with respect to the core plasma flow).
Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S601-S604. 〈10.1016/j.jnucmat.2010.10.073〉. 〈hal-00848536〉
Philippe Ghendrih, K. Bodi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, et al.. Transition to supersonic flows in the edge plasma. Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53 (5), pp.054019. 〈10.1088/0741-3335/53/5/054019〉. 〈hal-00848545〉 Plus de détails...
With a proper choice of a single dimensionless control parameter one describes the transition between subsonic and supersonic flows as a bifurcation. The bifurcation point is characterized by specific properties of the control parameter: the control parameter has a vanishing derivative in space and takes the maximum possible value equal to 1. This method is then applied to the sheath plasma with constant temperatures, allowing one to recover the Bohm boundary condition as well as the location of the point where the bifurcation takes place. This analysis is extended to fronts, rarefaction waves and divertor plasmas. Two cases are found, those where departure from quasineutrality is mandatory to generate a maximum in the variation of the control parameter (sheath and fronts) and those where the physics of the quasineutral plasma can generate such a maximum (rarefaction waves and supersonic flow in divertors). The conditions that are required to recover the Bohm condition, when modelling the wall using the penalization technique, are also addressed and generalized.
Philippe Ghendrih, K. Bodi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, et al.. Transition to supersonic flows in the edge plasma. Plasma Physics and Controlled Fusion, IOP Publishing, 2011, 53 (5), pp.054019. 〈10.1088/0741-3335/53/5/054019〉. 〈hal-00848545〉
E. Plaut, Y. Lebranchu, M. Jenny, Eric Serre. Structure and stability of annular sheared channel flows: effects of confinement, curvature and inertial forces - waves. European Physical Journal B: Condensed Matter and Complex Systems, Springer-Verlag, 2011, 79 (1), pp.35-46. 〈10.1140/epjb/e2010-10572-3〉. 〈hal-01023235〉 Plus de détails...
The structure and stability of the flows in an annular channel sheared by a rotating lid are investigated experimentally, theoretically and numerically. The channel has a square section, and a small curvature parameter: the ratio Γ of the inter-radii to the mean radius is 9.5%. The sidewalls and the bottom of the channel are integral and can rotate independently of the lid, permitting pure shear, co-rotation and counter-rotation cases. The basic flows obtained at small shear are characterized. In the absence of co-rotation, the centrifugal force linked with the curvature of the system plays an important role, whereas, when co-rotation is fast, the Coriolis force dominates. These basic flows undergo some instabilities when the shear is increased. These instabilities lead to supercritical traveling waves in the pure shear and co-rotation cases, but to weak turbulence in the counter-rotation case. The Reynolds number for the onset of instabilities, constructed with the velocity difference between the lid and bottom at mid-radius, and the height of the channel, increases from 1000 in the counter-rotation case to 1260 in the pure shear case and higher and higher values when co-rotation increases, i.e., when the Coriolis effect increases. The relevance of uni-dimensional Ginzburg-Landau models to describe the dynamics of the waves is studied. The domain of validity of these models turns out to be quite narrow.
E. Plaut, Y. Lebranchu, M. Jenny, Eric Serre. Structure and stability of annular sheared channel flows: effects of confinement, curvature and inertial forces - waves. European Physical Journal B: Condensed Matter and Complex Systems, Springer-Verlag, 2011, 79 (1), pp.35-46. 〈10.1140/epjb/e2010-10572-3〉. 〈hal-01023235〉
Journal: European Physical Journal B: Condensed Matter and Complex Systems
Eric Serre, M. Minguez, R., Pasquetti, G.B. Deng, M. Kornhass, et al.. On simulating the turbulent flow around the Ahmed body : A French-German collaborative evaluation of LES and DES. Computers and Fluids, Elsevier, 2011. 〈hal-01145131〉 Plus de détails...
Eric Serre, M. Minguez, R., Pasquetti, G.B. Deng, M. Kornhass, et al.. On simulating the turbulent flow around the Ahmed body : A French-German collaborative evaluation of LES and DES. Computers and Fluids, Elsevier, 2011. 〈hal-01145131〉
B. Viaud, Eric Serre, Jean-Marc Chomaz. Transition to turbulence through steep global-modes cascade in an open rotating cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2011, 688, pp.493-506. 〈10.1017/jfm.2011.393〉. 〈hal-00998000〉 Plus de détails...
B. Viaud, Eric Serre, Jean-Marc Chomaz. Transition to turbulence through steep global-modes cascade in an open rotating cavity. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2011, 688, pp.493-506. 〈10.1017/jfm.2011.393〉. 〈hal-00998000〉
A. Paredes, Eric Serre, Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, et al.. Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S579-S583. 〈10.1016/j.jnucmat.2010.12.247〉. 〈hal-00848532〉 Plus de détails...
Isoardi et al. [1] recently proposed a penalization technique to model solid plasma facing components that treats a solid obstacle as a sink region corresponding to the strong plasma recombination in the solid state material. A major advantage of this approach is that it produces a system that can be solved in an obstacle free domain, thus allowing the use of powerful numerical algorithms. Such a technique implemented in a minimal transport model for ionic density and parallel momentum appeared to exhibit a Mach-1 transition at the boundary layer between the plasma presheath and the limiter region. In this paper, we reconsider this result by analysing the physics of detached plasmas that are governed both by strong recombination and plasma pressure decrease, as imposed by the penalization technique within the limiter region. The analysis provides a unique control parameter A=Γcsmi/ΠA=Γcsmi/Π (Γ being the parallel particles flux, cs the sound speed, mi the ionic mass and Π the total plasma pressure) that allows one to understand the results of the penalization technique for the Mach-1 transition.
A. Paredes, Eric Serre, Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, et al.. Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S579-S583. 〈10.1016/j.jnucmat.2010.12.247〉. 〈hal-00848532〉
Guilhem Dif-Pradalier, J Gunn, Guido Ciraolo, C Chang, Guillaume Chiavassa, et al.. The Mistral base case to validate kinetic and fluid turbulence transport codes of the edge and SOL plasmas. Journal of Nuclear Materials, Elsevier, 2011, 415, 〈10.1016/j.jnucmat.2010.12.035〉. 〈cea-01468372〉 Plus de détails...
Experimental data from the Tore Supra experiments are extrapolated in the SOL and edge to investigate the Kelvin–Helmholtz instability. The linear analysis indicates that a large part of the SOL is rather unstable. The effort is part of the setup of the Mistral base case that is organised to validate the codes and address new issues on turbulent edges, including the comparison of kinetic and fluid modelling in the edge plasma.
Guilhem Dif-Pradalier, J Gunn, Guido Ciraolo, C Chang, Guillaume Chiavassa, et al.. The Mistral base case to validate kinetic and fluid turbulence transport codes of the edge and SOL plasmas. Journal of Nuclear Materials, Elsevier, 2011, 415, 〈10.1016/j.jnucmat.2010.12.035〉. 〈cea-01468372〉
Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, Pierre Haldenwang, Eric Serre, et al.. Penalization modeling of a limiter in the Tokamak edge plasma. Journal of Computational Physics, Elsevier, 2010, 229 (6), pp.2220-2235. 〈10.1016/j.jcp.2009.11.031〉. 〈hal-00386101v2〉 Plus de détails...
An original penalization method is applied to model the interaction of magnetically confined plasma with limiter in the frame of minimal transport model for ionic density and parallel momentum. The limiter is considered as a pure particle sink for the plasma and consequently the density and the momentum are enforced to be zero inside. Comparisons of the numerical results with one dimensional analytical solutions show a very good agreement. In particular, presented method provides a plasma velocity which is almost sonic at the boundaries obstacles as expected from the sheath conditions through the Bohm criterion. The new system being solved in an obstacle free domain, an efficient pseudo-spectral algorithm based on a Fast Fourier transform is also proposed, and associated with an exponential filtering of the unphysical oscillations due to Gibbs phenomenon. Finally, the efficiency of the method is illustrated by investigating the flow spreading from the plasma core to the Scrape Off Layer at the wall in a two-dimensional system with one then two limiters neighboring.
Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, Pierre Haldenwang, Eric Serre, et al.. Penalization modeling of a limiter in the Tokamak edge plasma. Journal of Computational Physics, Elsevier, 2010, 229 (6), pp.2220-2235. 〈10.1016/j.jcp.2009.11.031〉. 〈hal-00386101v2〉
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Pressure-driven radial flow in a Taylor-Couette cell. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2010, 660, pp.527-537. 〈10.1017/S0022112010003228〉. 〈hal-01024690〉 Plus de détails...
A generalized solution for pressure-driven flow through a permeable rotating inner cylinder in an impermeable concentric outer cylinder, a situation used commercially in rotating filtration, is challenging due to the interdependence between the pressure drop in the axial direction and that across the permeable inner cylinder. Most previous approaches required either an imposed radial velocity at the inner cylinder or radial throughflow with both the inner and outer cylinders being permeable. We provide an analytical solution for rotating Couette-Poiseuille flow with Darcy's law at the inner cylinder by using a small parameter related to the permeability of the inner cylinder. The theory works for suction, injection and even combined suction/injection, when the axial pressure drop in the annulus is such that the transmembrane pressure difference reverses sign along the axial extent of the system. Corresponding numerical simulations for finite-length systems match the theory very well.
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Pressure-driven radial flow in a Taylor-Couette cell. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2010, 660, pp.527-537. 〈10.1017/S0022112010003228〉. 〈hal-01024690〉
Brian Launder, Sébastien Poncet, Eric Serre. Laminar, transitional, and turbulent flows in rotor-stator cavities. Annual Review of Fluid Mechanics, Annual Reviews, 2010, 42 (1), pp.229-248. 〈10.1146/annurev-fluid-121108-145514〉. 〈hal-00678846〉 Plus de détails...
This article reviews the range of flows that may be created within thin cylindrical or annular cavities due to the rotation of one of the confining disks. At low Reynolds numbers, the rotation gives rise to an axisymmetric, radially outward motion near the rotor with a return flow along the stationary disk. As the Reynolds number is raised, this base flow gives way to a shear flow populated by discrete vortices, whether of cylindrical or spiral form, near both the rotating and stationary disks. At Reynolds numbers high enough for turbulent flow to occur, in the twentieth century both experimental and computational studies treated the flow as axisymmetric and steady. Recent research has shown, however, that complex organized structures also persist in the turbulent regime.
Brian Launder, Sébastien Poncet, Eric Serre. Laminar, transitional, and turbulent flows in rotor-stator cavities. Annual Review of Fluid Mechanics, Annual Reviews, 2010, 42 (1), pp.229-248. 〈10.1146/annurev-fluid-121108-145514〉. 〈hal-00678846〉
Sébastien Poncet, Eric Serre. High-order LES of turbulent heat transfer in a rotor–stator cavity. International Journal of Heat and Fluid Flow, Elsevier, 2009, 30, pp.590-601. 〈10.1016/j.ijheatfluidflow.2009.01.011〉. 〈hal-00409169〉 Plus de détails...
The present work examines the turbulent flow in an enclosed rotor–stator system subjected to heat transfer effects. Besides their fundamental importance as three-dimensional prototype flows, such flows arise in many industrial applications but also in many geophysical and astrophysical settings. Large eddy simulations(LES) are here performed using a spectral vanishing viscosity technique. The LES results have already been favorably compared to velocity measurements in the isothermal case (Séverac et al. 2007) for a large range of Reynolds numbers in an annular cavity of large aspect ratio and weak curvature parameter. The purpose of this paper is to extend these previous results in the non-isothermal case using the Boussinesq approximation to take into account the buoyancy effects. Thus, the effects of thermal convection have been examined for a turbulent flow of air in the same rotor–stator system for Rayleigh numbers up to 100 millions. These LES results provide accurate, instantaneous quantities which are of interest in understanding the physics of turbulent flows and heat transfers in an interdisk cavity. Even at high Rayleigh numbers, the structure of the iso-values of the instantaneous normal temperature gradient at the disk surfaces resembles the one of the iso-values of the tangential velocity with large spiral arms along the rotor and more thin structures along the stator. The averaged results show small effects of density variation on the mean and turbulent fields. The turbulent Prandtl number is a decreasing function of the distance to the wall with 1.4 close to the disks and about 0.3 in the outer layers. The local Nusselt number is found to be proportional to the local Reynolds number to the power 0.7. The evolution of the averaged Bolgiano length scale with the Rayleigh number indicates that temperature fluctuations may have a large influence on the dynamics only at the largest scales of the system for Ra larger than 10 millions, since the averaged Bolgiano length scale remains lower than the thermal boundary layer thicknesses.
Sébastien Poncet, Eric Serre. High-order LES of turbulent heat transfer in a rotor–stator cavity. International Journal of Heat and Fluid Flow, Elsevier, 2009, 30, pp.590-601. 〈10.1016/j.ijheatfluidflow.2009.01.011〉. 〈hal-00409169〉
Journal: International Journal of Heat and Fluid Flow