Simulations avancées de turbulence pariétale à haut nombre de Reynolds sur des géométries curvilignes par une approche hybride RANS/LES

The ability to simulate the dynamics of turbulent boundary layers is essential for the prediction of the unsteady aerodynamic and aeroacoustic properties of both land and air vehicles. Therefore, the present work proposes an innovative method to simulate near wall flows, around curvilinear geometries at high Reynolds numbers. The "Wall Modelled Large Eddy Simulation" mode of the ZDES method is considered here. First of all, a turbulence reactivation method, based on the combination of a synthetic turbulence injection method and of a body forcing one, is developed in order to allow a local WMLES resolution of the regions of interest within an essentially RANS calculation. Therefore, the study of the interactions that exist between the physics and the ZDES numerical method, in the case of a zero pressure gradient turbulent boundary layer developing over a flat plate until Re=13 000, led to a generalization of the guide lines to use the WMLES mode of the ZDES. Advanced unsteady post-processing enabled to demonstrate the ability of the method to simulate the specific dynamics of the outer region at high Reynolds numbers. Finally, the various methods that have been developed during this study were applied to the simulation of a S-shaped duct of rectangular section. The multi-scale dynamic of this flow as well as its resulting distortions were successfully simulated thanks to this new method, for an overall cost reduction of about 50 times compared to a traditional LES approachLa capacité de simuler la dynamique de la couche limite turbulente représente aujourd'hui un enjeu important pour la prévision de l'aérodynamique instationnaire et de l'aéroacoustique des aéronefs et des véhicules terrestres. Aussi, les travaux présentés dans ce manuscrit proposent une méthode originale de simulation de la dynamique des écoulements turbulents pariétaux, à haut nombre de Reynolds, sur des géométries curvilignes. L'approche ZDES, dans son mode " Wall Modelled Large Eddy Simulation ", est ici retenue. Dans un premier temps, une méthode de réactivation turbulente, par combinaison de l'injection de turbulence synthétique et de l'application de termes de forçage, est développée afin de permettre une résolution WMLES locale des régions d'intérêt au sein d'une simulation majoritairement RANS. Puis l'étude des interactions entre la physique et la méthode de résolution numérique (ZDES), sur le cas d'une couche limite turbulente sans gradient de pression en développement spatial jusqu'à Re13 000, a conduit à une généralisation des conditions d'emploi du mode WMLES de la ZDES. Des post-traitements instationnaires avancés ont permis de démontrer la capacité de la méthode à simuler la dynamique particulière de la zone externe à ces grands nombres de Reynolds. Enfin, les différentes méthodes développées au cours de cette étude ont été appliquées à la simulation d'une manche à air coudée de section rectangulaire. Cette nouvelle méthode a permis de simuler avec succès la dynamique multi-échelles de cet écoulement et des distorsions dynamiques associées, pour un coût environ 50 fois inférieur à celui d'une approche LES classiqu

Simulations avancées de turbulence pariétale à haut nombre de Reynolds sur des géométries curvilignes par une approche hybride RANS/LES

La capacité de simuler la dynamique de la couche limite turbulente représente aujourd hui un enjeu important pour la prévision de l aérodynamique instationnaire et de l aéroacoustique des aéronefs et des véhicules terrestres. Aussi, les travaux présentés dans ce manuscrit proposent une méthode originale de simulation de la dynamique des écoulements turbulents pariétaux, à haut nombre de Reynolds, sur des géométries curvilignes. L approche ZDES, dans son mode Wall Modelled Large Eddy Simulation , est ici retenue. Dans un premier temps, une méthode de réactivation turbulente, par combinaison de l injection de turbulence synthétique et de l application de termes de forçage, est développée afin de permettre une résolution WMLES locale des régions d intérêt au sein d une simulation majoritairement RANS. Puis l étude des interactions entre la physique et la méthode de résolution numérique (ZDES), sur le cas d une couche limite turbulente sans gradient de pression en développement spatial jusqu à Re 13 000, a conduit à une généralisation des conditions d emploi du mode WMLES de la ZDES. Des post-traitements instationnaires avancés ont permis de démontrer la capacité de la méthode à simuler la dynamique particulière de la zone externe à ces grands nombres de Reynolds. Enfin, les différentes méthodes développées au cours de cette étude ont été appliquées à la simulation d une manche à air coudée de section rectangulaire. Cette nouvelle méthode a permis de simuler avec succès la dynamique multi-échelles de cet écoulement et des distorsions dynamiques associées, pour un coût environ 50 fois inférieur à celui d une approche LES classiqueThe ability to simulate the dynamics of turbulent boundary layers is essential for the prediction of the unsteady aerodynamic and aeroacoustic properties of both land and air vehicles. Therefore, the present work proposes an innovative method to simulate near wall flows, around curvilinear geometries at high Reynolds numbers. The Wall Modelled Large Eddy Simulation mode of the ZDES method is considered here. First of all, a turbulence reactivation method, based on the combination of a synthetic turbulence injection method and of a body forcing one, is developed in order to allow a local WMLES resolution of the regions of interest within an essentially RANS calculation. Therefore, the study of the interactions that exist between the physics and the ZDES numerical method, in the case of a zero pressure gradient turbulent boundary layer developing over a flat plate until Re =13 000, led to a generalization of the guide lines to use the WMLES mode of the ZDES. Advanced unsteady post-processing enabled to demonstrate the ability of the method to simulate the specific dynamics of the outer region at high Reynolds numbers. Finally, the various methods that have been developed during this study were applied to the simulation of a S-shaped duct of rectangular section. The multi-scale dynamic of this flow as well as its resulting distortions were successfully simulated thanks to this new method, for an overall cost reduction of about 50 times compared to a traditional LES approachPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

A dynamic forcing method for unsteady turbulent inflow conditions

International audienceThe present paper aims to provide an efficient and flexible method for the initialization of a zonal RANS/LES type calculation when the resolution of the near wall region is treated in RANS mode. Indeed, when part of the boundary layer must be resolved in LES mode, one generally experiences a very long transient state, which makes this approach inapplicable to industrial applications. The skillful combination of a Zonal Detached Eddy Simulation method (ZDES), a Synthetic Eddy Method (SEM) and a self-adaptative dynamic forcing approach enables this. The two former being taken as framework, while the latter, based on innovative considerations, is the purpose of the paper. The main strength of the dynamic forcing method comes from its local nature, enabling to treat geometrically complex applications.A new definition of the dynamic forcing method, based on View the MathML sourcev′2¯t error, is derived from the original one. It dramatically increases the efficiency of the inflow generation. Indeed, the dynamic forcing method allows to reduce the transition distance up to 76%, compared to the SEM inflow by itself, when a RANS/LES type resolution is employed. Thus the use of a synthetic turbulence generation method is now affordable for industrial applications both technically and economically. A particular attention is brought to the behavior and the parametrization of such an approach, with regards to the other simulation parameters. The authors will try to give all the information required to successfully apply the present strategy on a particular case

Tetrahedral Remeshing in the Context of Large-Scale Numerical Simulation and High Performance Computing

The purpose of this article is to discuss several modern aspects of remeshing, which is the task of modifying an ill-shaped tetrahedral mesh with bad size elements so that it features an appropriate density of high-quality elements. After a brief sketch of classical stakes about meshes and local mesh operations, we notably expose (i) how the local size of the elements of a mesh can be adapted to a user-defined prescription (guided, e.g., by an error estimate attached to a numerical simulation), (ii) how a mesh can be deformed to efficiently track the motion of the underlying domain, (iii) how to construct a mesh of an implicitlydefined domain, and (iv) how remeshing procedures can be conducted in a parallel fashion when large-scale applications are targeted. These ideas are illustrated with several applications involving high-performance computing. In particular, we show how mesh adaptation and parallel remeshing strategies make it possible to achieve a high accuracy in large-scale simulations of complex flows, and how the aforementioned methods for meshing implicitly defined surfaces allow to represent faithfully intricate geophysical interfaces, and to account for the dramatic evolutions of shapes featured by shape optimization processes

Tetrahedral Remeshing in the Context of Large-Scale Numerical Simulation and High Performance Computing

The purpose of this article is to discuss several modern aspects of remeshing, which is the task of modifying an ill-shaped tetrahedral mesh with bad size elements so that it features an appropriate density of high-quality elements. After a brief sketch of classical stakes about meshes and local mesh operations, we notably expose (i) how the local size of the elements of a mesh can be adapted to a user-defined prescription (guided, e.g., by an error estimate attached to a numerical simulation), (ii) how a mesh can be deformed to efficiently track the motion of the underlying domain, (iii) how to construct a mesh of an implicitlydefined domain, and (iv) how remeshing procedures can be conducted in a parallel fashion when large-scale applications are targeted. These ideas are illustrated with several applications involving high-performance computing. In particular, we show how mesh adaptation and parallel remeshing strategies make it possible to achieve a high accuracy in large-scale simulations of complex flows, and how the aforementioned methods for meshing implicitly defined surfaces allow to represent faithfully intricate geophysical interfaces, and to account for the dramatic evolutions of shapes featured by shape optimization processes