A cell-centered pressure-correction scheme for the compressible Euler equations

We propose a robust pressure-correction scheme for the numerical solution of the compressible Euler equations discretized by a colocated finite volume method. The scheme is based on an internal energy formulation, which ensures that the internal energy is positive. More generally, the scheme enjoys fundamental stability properties: without restriction on the time step, both the density and the internal energy are positive, the integral of the total energy over the computational domain is preserved thanks to an estimate on the discrete kinetic energy, and a discrete entropy ineqality is satisfied. These stability properties ensure the existence of a solution to the scheme. The internal energy balance features a corrective source term which is needed for the scheme to compute the correct shock solutions: we are indeed able to prove a Lax-type convergence result, in the sense that, under some compactness assumptions, the limit of a converging sequence of approximate solutions obtained with space and time discretization steps tending to zero is an entropy weak solution of the Euler equations. The obtained theoretical results and the scheme accuracy are verified ny numerical experiments; in particular, the qualitative behaviour of the scheme is assessed on 1D and 2D Riemann problems and compared with other schemes

Contribution to numerical methods for all Mach flow regimes and to fluid-porous coupling for the simulation of homogeneous two-phase flows in nuclear reactors

Le calcul d'écoulements dans les générateurs de vapeur des réacteurs à eau pressurisée est un problème complexe, faisant intervenir différents régimes d'écoulement et plusieurs échelles de temps et d'espace. Un scénario accidentel peut être caractérisé par des variations très rapides pour un nombre de Mach de l'ordre de l'unité. A l'inverse en régime nominal l'écoulement peut être stationnaire, à bas nombre de Mach. De plus quelque soit le régime considéré, la complexité de la géométrie d'un générateur de vapeur conduit à modéliser le faisceau de tubes par un milieu poreux, d'où le problème de couplage à l'interface avec le milieu fluide.Un schéma de correction de pression tout-Mach en volumes finis colocalisés a été introduit pour les équations d'Euler et de Navier-Stokes. L'existence d'une solution discrète, la consistance du schéma au sens de Lax et la positivité de l'énergie interne ont été démontrées. Le schéma a été ensuite étendu aux modèles diphasiques homogènes du code GENEPI développé au CEA. Enfin un algorithme Multigrille-AMR a été adaptée pour permettre de mettre en oeuvre notre schéma sur des maillages adaptatifs.Concernant la seconde problématique, une extension de la loi de Beavers-Joseph a été proposée pour le régime convectif. En introduisant un saut d'énergie cinétique à l'interface, on retrouve une loi de type Beavers-Joseph mais avec un coefficient de glissement non-linéaire, qui dépend de la vitesse fluide à l'interface et de la vitesse Darcy. La validité de cette nouvelle condition d'interface a été évaluée en réalisant des calculs de simulation numérique directe à différents nombres de Reynolds.The numerical simulation of steam generators of pressurized water reactors is a complex problem, involving different flow regimes and a wide range of length and time scales. An accidental scenario may be associated with very fast variations of the flow with an important Mach number. In contrast in the nominal regime the flow may be stationary, at low Mach number. Moreover whatever the regime under consideration, the array of U-tubes is modelled by a porous medium in order to avoid taking into account the complex geometry of the steam generator, which entails the issue of the coupling conditions at the interface with the free-fluid.We propose a new pressure-correction scheme for cell-centered finite volumes for solving the compressible Navier-Stokes and Euler equations at all Mach number. The existence of a discrete solution, the consistency of the scheme in the Lax sense and the positivity of the internal energy were proved. Then the scheme was extended to the homogeneous two-phase flow models of the GENEPI code developed at CEA. Lastly a multigrid-AMR algorithm was adapted for using our pressure-correction scheme on adaptive grids.Regarding the second issue addressed in this work, an extension to the Beavers-Joseph law was proposed for the convective regime. By introducing a jump in the kinetic energy at the interface, we recover an interface condition close to the Beavers-Joseph law but with a non-linear slip coefficient, which depends on the free-fluid velocity at the interface and on the Darcy velocity. The validity of this new transmission condition was assessed with direct numerical simulations at different Reynolds numbers

Contribution à la résolution numérique d'écoulements à tout nombre de Mach et au couplage fluide-poreux en vue de la simulation d'écoulements diphasiques homogénéisés dans les composants nucléaires

The numerical simulation of steam generators of pressurized water reactors is a complex problem, involving different flow regimes and a wide range of length and time scales. An accidental scenario may be associated with very fast variations of the flow with an important Mach number. In contrast in the nominal regime the flow may be stationary, at low Mach number. Moreover whatever the regime under consideration, the array of U-tubes is modelled by a porous medium in order to avoid taking into account the complex geometry of the steam generator, which entails the issue of the coupling conditions at the interface with the free-fluid.We propose a new pressure-correction scheme for cell-centered finite volumes for solving the compressible Navier-Stokes and Euler equations at all Mach number. The existence of a discrete solution, the consistency of the scheme in the Lax sense and the positivity of the internal energy were proved. Then the scheme was extended to the homogeneous two-phase flow models of the GENEPI code developed at CEA. Lastly a multigrid-AMR algorithm was adapted for using our pressure-correction scheme on adaptive grids.Regarding the second issue addressed in this work, the numerical simulation of a fluid flow over a porous bed involves very different length scales. Macroscopic interface models --- such as Ochoa-Tapia--Whitaker or Beavers-Joseph law for a viscous flow --- represent the transition region between the free-fluid and the porous region by an interface of discontinuity associated with specific transmission conditions. An extension to the Beavers-Joseph law was proposed for the convective regime. By introducing a jump in the kinetic energy at the interface, we recover an interface condition close to the Beavers-Joseph law but with a non-linear slip coefficient, which depends on the free-fluid velocity at the interface and on the Darcy velocity. The validity of this new transmission condition was assessed with direct numerical simulations at different Reynolds numbers.Le calcul d'écoulements dans les générateurs de vapeur des réacteurs à eau pressurisée est un problème complexe, faisant intervenir différents régimes d'écoulement et plusieurs échelles de temps et d'espace. Un scénario accidentel peut être caractérisé par des variations très rapides pour un nombre de Mach de l'ordre de l'unité. A l'inverse en régime nominal l'écoulement peut être stationnaire, à bas nombre de Mach. De plus quelque soit le régime considéré, la complexité de la géométrie d'un générateur de vapeur conduit à modéliser le faisceau de tubes par un milieu poreux, d'où le problème de couplage à l'interface avec le milieu fluide.Un schéma de correction de pression tout-Mach en volumes finis colocalisés a été introduit pour les équations d'Euler et de Navier-Stokes à tout nombre de Mach. L'existence d'une solution discrète, la consistance du schéma au sens de Lax et la positivité de l'énergie interne ont été démontrées. Le schéma a été ensuite étendu aux modèles diphasiques homogènes du code GENEPI développé au CEA. Enfin un algorithme Multigrille-AMR a été adaptée pour permettre de mettre en oeuvre notre schéma sur des maillages adaptatifs.Concernant la seconde problématique, une extension de la loi de Beavers-Joseph a été proposée pour le régime convectif. En introduisant un saut d'énergie cinétique à l'interface, on retrouve une loi de type Beavers-Joseph mais avec un coefficient de glissement non-linéaire, qui dépend de la vitesse fluide à l'interface et de la vitesse Darcy. La validité de cette nouvelle condition d'interface a été évaluée en réalisant des calculs de simulation numérique directe à différents nombres de Reynolds

A cell-centered pressure-correction scheme for the compressible Euler equations

International audienceWe propose a robust pressure-correction scheme for the numerical solution of the compressible Euler equations discretized by a colocated finite volume method. The scheme is based on an internal energy formulation, which ensures that the internal energy is positive. More generally, the scheme enjoys fundamental stability properties: without restriction on the time step, both the density and the internal energy are positive, the integral of the total energy over the computational domain is preserved thanks to an estimate on the discrete kinetic energy, and a discrete entropy ineqality is satisfied. These stability properties ensure the existence of a solution to the scheme. The internal energy balance features a corrective source term which is needed for the scheme to compute the correct shock solutions: we are indeed able to prove a Lax-type convergence result, in the sense that, under some compactness assumptions, the limit of a converging sequence of approximate solutions obtained with space and time discretization steps tending to zero is an entropy weak solution of the Euler equations. The obtained theoretical results and the scheme accuracy are verified ny numerical experiments; in particular, the qualitative behaviour of the scheme is assessed on 1D and 2D Riemann problems and compared with other schemes

A cell-centered pressure-correction scheme for the compressible Euler equations

International audienceWe propose a robust pressure-correction scheme for the numerical solution of the compressible Euler equations discretized by a colocated finite volume method. The scheme is based on an internal energy formulation, which ensures that the internal energy is positive. More generally, the scheme enjoys fundamental stability properties: without restriction on the time step, both the density and the internal energy are positive, the integral of the total energy over the computational domain is preserved thanks to an estimate on the discrete kinetic energy, and a discrete entropy ineqality is satisfied. These stability properties ensure the existence of a solution to the scheme. The internal energy balance features a corrective source term which is needed for the scheme to compute the correct shock solutions: we are indeed able to prove a Lax-type convergence result, in the sense that, under some compactness assumptions, the limit of a converging sequence of approximate solutions obtained with space and time discretization steps tending to zero is an entropy weak solution of the Euler equations. The obtained theoretical results and the scheme accuracy are verified ny numerical experiments; in particular, the qualitative behaviour of the scheme is assessed on 1D and 2D Riemann problems and compared with other schemes

A PARALLEL IMPLEMENTATION OF THE MORTAR ELEMENT METHOD IN 2D AND 3D

Abstract. We present here the generic parallel computational framework in C++ called Feel++ for the mortar finite element method with the arbitrary number of subdomain partitions in 2D and 3D. An iterative method with block-diagonal preconditioners is used for solving the algebraic saddle-point problem arising from the finite element discretization. Finally we present a scalability study and the numerical results obtained using Feel++ library