Liang Shao - Academia.edu (original) (raw)
Papers by Liang Shao
Physics of Fluids, 2009
The velocity increment (VI) model, which was introduced by Brun et al., is improved by employing ... more The velocity increment (VI) model, which was introduced by Brun et al., is improved by employing the Kolmogorov equation of filtered velocity in this paper. This model has two different formulations: a dynamic formulation and a simplified constant form in high Reynolds number turbulence. A priori tests in isotropic turbulence and wall-bounded turbulence are performed. A posteriori tests of decaying turbulence and channel Poiseuille flow are made to testify the model performance, especially on the energy backscatter. The simple constant coefficient formulation has good performance, and avoids the ensemble average operation, which exists in other subgrid models. This constant improved VI model is particularly proposed in complicated large-eddy simulation projects.
Journal of Fluid Mechanics, 2007
A new subgrid eddy-viscosity model is proposed in this paper. Full details of the derivation of t... more A new subgrid eddy-viscosity model is proposed in this paper. Full details of the derivation of the model are given with the assumption of homogeneous turbulence. The formulation of the model is based on the dynamic equation of the structure function of resolved scale turbulence. By means of the local volume average, the effect of the anisotropy is taken into account in the generalized Kolmogorov equation, which represents the equilibrium energy transfer in the inertial subrange. Since the proposed model is formulated directly from the filtered Navier–Stokes equation, the resulting subgrid eddy viscosity has the feature that it can be adopted in various turbulent flows without any adjustments of model coefficient. The proposed model predicts the major statistical properties of rotating turbulence perfectly at fairly low-turbulence Rossby numbers whereas subgrid models, which do not consider anisotropic effects in turbulence energy transfer, cannot predict this typical anisotropic tu...
Acta Mechanica Sinica, 2014
Eddy-damping quasinormal Markovian (EDQNM) theory is employed to calculate the resolved-scale spe... more Eddy-damping quasinormal Markovian (EDQNM) theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scaling law of the resolved-scale turbulence, which is affected by several factors, is far from that of the full-scale turbulence and should be corrected. These results are then applied to an existing subgrid model to improve its performance. A series of simulations are performed to verify the necessity of a fixed scaling law in the subgrid modeling. Keywords Scaling law • Large-eddy simulation • CZZS model 1 Introduction Kolmogorov introduced the 2/3 scaling law for the secondorder structure function in isotropic turbulence, which is
Journal of Thermal Science, 2007
Large-eddy simulation developments and validations are presented for an improved simulation of tu... more Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria: numerical qualities (precision and spectral characteristics), and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and "low-cost" shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2015
The present study carried out a pure large eddy simulation (LES) on a NACA65 linear compressor ca... more The present study carried out a pure large eddy simulation (LES) on a NACA65 linear compressor cascade (chord-based Reynolds number: 382 000), at an incidence angle of 4°. In this configuration, a corner separation at the juncture of the blade suction side and the end-wall is clearly observed experimentally. For the simulation, 852 CPUs are used in parallel and particular attention is paid to the inflow conditions, coupling LES with the calculation of the inlet boundary layer and associated velocity fluctuations. The shear-improved Smagorinsky model, which has been proved to be competent for turbomachines, is used in this study. Numerical results are carefully compared with pressure measurements, two-dimensional and stereo particle image velocimetry. LES is found to be superior to Reynolds-averaged Navier–Stokes approach in predicting the three-dimensional separated flows in the compressor cascade since pressure coefficients and losses are in very good agreement with the experiment....
Physics of Fluids, 1999
Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer ... more Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer flows at high Reynolds number with mean wall shear stress boundary condition
Physics of Fluids, 1999
Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer ... more Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer flows at high Reynolds number with mean wall shear stress boundary condition
Physics of Fluids, 1999
Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer ... more Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer flows at high Reynolds number with mean wall shear stress boundary condition
Journal of Fluid Mechanics, 2007
A shear-improved Smagorinsky model is introduced based on results concerning mean-shear effects i... more A shear-improved Smagorinsky model is introduced based on results concerning mean-shear effects in wall-bounded turbulence. The Smagorinsky eddy-viscosity is modified asvT=(Csδ)2(|S|—|〈S〉|): the magnitude of the mean shear |〈S〉|is subtracted from the magnitude of the instantaneous resolved rate-of-strain tensor |S|;CSis the standard Smagorinsky constant and Δ denotes the grid spacing. This subgrid-scale model is tested in large-eddy simulations of plane-channel flows at Reynolds numbersReτ= 395 andReτ= 590. First comparisons with the dynamic Smagorinsky model and direct numerical simulations for mean velocity, turbulent kinetic energy and Reynolds stress profiles, are shown to be extremely satisfactory. The proposed model, in addition to being physically sound and consistent with the scale-by-scale energy budget of locally homogeneous shear turbulence, has a low computational cost and possesses a high potential for generalization to complex non-homogeneous turbulent flows.
Springer Proceedings in Physics
Abstract. The aim of the study is to compare the LES of corner separation, considered as a refere... more Abstract. The aim of the study is to compare the LES of corner separation, considered as a reference, in the LMFA-NACA65 linear compressor cascade to RANS simulations using Wilcox two-equation models (k − ω). The LES was carried-out by Gao et al. [1] using the Shearimproved Smagorinsky model (SISM), and has been validated by comparison with the experimental data obtained by Ma et al. [2]. Two steady RANS simulations are carried out using k− ω models: Wilcox 1988 model and Wilcox 1988 model with quadratic constitutive relation. First, the analysis will consider the total pressure losses on a two-dimensional section downstream of the cascade. The Reynolds stresses and the turbulent kinetic energy budget are analysed within the separation region, on a two-dimensional section at the trailing edge of the blade. The RANS simulations mostly overestimate the total pressure losses and the size of the corner separation, compared to the LES and the experiment. The RANS simulations also overest...
Direct and Large-Eddy Simulation VII
ABSTRACT The velocity increment (VI) model of Brun et al. is improved by employing the Kolmogorov... more ABSTRACT The velocity increment (VI) model of Brun et al. is improved by employing the Kolmogorov equation of filtered velocity (KEF). The dynamic model coefficient is derived. In high Reynolds number turbulence, it is simplified in a constant form. A priori and a posteriori tests are made to testify the model performance. The constant coefficient form is low-cost and recommended.
12th European Conference on Turbomachinery Fluid Dynamics and hermodynamics
This study aims at analyzing the modeling of turbulence in a tip-leakage flow. The academic confi... more This study aims at analyzing the modeling of turbulence in a tip-leakage flow. The academic configuration considered is made of a single airfoil and a flat casing, with clearance, at Re=9.3e5. For characterising the turbulence, a zonal large-eddy simulation (ZLES), validated against experimental data, is considered as reference. ZLES was previously shown to describe precisely the flow features in the tip region, including the Reynolds stresses. Two steady Reynolds-averaged Navier-Stokes (RANS) simulations, using Wilcox's k-ω model, are evaluated against this reference. The first simulation uses the Boussinesq constitutive relation, whereas the second simulation relies on the quadratic constitutive relation (QCR). The analysis focuses on the mean velocities, the Reynolds stresses and a term-to-term decomposition of the turbulent kinetic energy budget. RANS is shown to underestimate the vorticity of the flow, the Reynolds stresses and the turbulent kinetic energy budget terms. The QCR has little effects on these deficits. KEYWORDS TIP-LEAKAGE FLOW, SINGLE AIRFOIL, RANS, LES, REYNOLDS STRESSES, TURBULENT KINETIC ENERGY BUDGET NOMENCLATURE M Mach number ∆x + , ∆y + , ∆z + Cell sizes at the wall, in wall O Normalized rotation tensor units Re c Reynolds number based on Π Sub-grid scale stress tensor the chord length of the blade Ξ Numerical residual tensor U Free-stream velocity δ ij Kroeneker symbol c Chord-length of the blade ρ Density h Tip-clearance height τ Viscous stress tensor k Turbulent kinetic energy τ t \τ QCR t Reynolds stress tensor with p Pressure Boussinesq constitutive u 1 , u 2 , u 3 Stream-wise (resp. transverse relation \with QCR and span-wise) velocities ω Turbulent kinetic energy x 1 , x 2 , x 3 Stream-wise (resp. transverse specific dissipation rate and span-wise) directions
Computers & Fluids
The generation of turbulent inflow conditions in large-eddy simulation (LES) is a key ingredient ... more The generation of turbulent inflow conditions in large-eddy simulation (LES) is a key ingredient for general applications of LES in both academic turbulent flows and industrial designs with complicated engineering flows. This is because accurate predictions of the fluid behaviour are strongly dependent on the inflow conditions, particularly in turbulent flows at high turbulent Reynolds numbers. This paper aims at improving the vortex method (VM) of Sergent [1] that demands long adaptive distances (12 times the half channel height, for a channel flow at Re τ = 395) to achieve high quality turbulence, and evaluating the equilibrium of the flow field obtained in terms of both the equilibrium of the mean flow and that of the turbulence (inter-scale turbulent energy transfer). The mean flow equilibrium is checked with classic criteria such as the friction velocity. In order to assess the equilibrium of turbulence, we propose using the velocity-derivative skewness, because it associates with the balance of energy transfer between large-and small-scale fluid motions. Numerical tests with the optimised set of model parameters reveal that the IVM is very efficient, in terms of adaptive distance, in generating high-quality synthetic turbulent fluctuations over a moderate distance: 6h for channel flow and 21δ for flat-plate boundary layer, with h and δ being respectively the half channel height and the nominal boundary layer thickness.
Http Www Theses Fr, 1992
Le travail de cette these est une contribution a l'etude de la turbulence inhomogene et s'... more Le travail de cette these est une contribution a l'etude de la turbulence inhomogene et s'inscrit dans le cadre d'etude a finalite aeronautique. Il s'agit d'une approche, par simulation numerique directe des grandes echelles de la turbulence, de l'interaction de deux turbulences d'echelles et de niveaux energetiques differents, placees cote a cote a l'instant initial et evoluant librement sans gradient de vitesse moyenne. Une telle situation physique constitue le cas le plus simple pour l'etude des phenomenes de transport spatial de turbulence, une seule direction d'inhomogeneite etant presente. Le but essentiel de l'etude est de completer les resultats experimentaux fournis par un travail effectue par Warhaft a l'universite de Cornell, contribuant par la a une meilleure comprehension de mecanismes physiques encore mal pris en compte dans les modeles simples. Les resultats de simulation montrent un bon accord qualitatif avec l'experience existante. De plus, des informations non accessibles experimentalement sont obtenues. Ce sont les correlations triples de vitesse qui assurent le transport de turbulence, tandis que la correlation pression vitesse tend a contrebalancer legerement ce transport. Le mecanisme de transport de turbulence est maintenant mieux compris, notamment en ce qui concerne le role joue par l'intermittence. Dans un but pratique d'applications industrielles, les resultats de simulation sont compares a ceux obtenus dans la meme situation par des modeles de turbulence simples (modeles en un point). Les comparaisons montrent que les modeles classiques ne prennent pas en compte le mecanisme de l'intermittence. Une modification des modeles classiques est introduite et les resultats se trouvent ameliores. L’etude a ensuite ete etendue au cas ou la couche de melange turbulente est soumise a une rotation en bloc. Les resultats montrent que la force de Coriolis modifie de facon considerable le mecanisme de transport. Deux effets sont identifies; les correlations triples sont fortement inhibees; la correlation pression vitesse assure le transport. Le premier effet a ete modelise; tandis que la prise en compte du second effet dans les modeles simples reste un probleme ouvert
ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C, 2010
In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anis... more In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anisotropy affect the subgrid stress via the mean flow gradient. A method of evaluating the mean effects is to split the subgrid stress tensor into “rapid” and “slow” parts. This decomposition was introduced by Shao et al. (1999) and applied to A Priori tests of existing subgrid models in the case of a turbulent mixing layer. In the present work, the decomposition is extended to the case of a passive scalar in inhomogeneous turbulence. The contributions of rapid and slow subgrid scalar flux, both in the equations of scalar variance and scalar flux, are analyzed. A Priori numerical tests are performed in a turbulent Couette flow with a mean scalar gradient. Results are then used to evaluate the performances of different popular subgrid scalar models. It is shown that existing models can not well simulate the slow part and need to be improved. In order to improve the modeling, an extension of ...
Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 1998
The present study sheds light on the subgrid modeling problem encountered in large eddy simulatio... more The present study sheds light on the subgrid modeling problem encountered in large eddy simulation (LES) of practical flows where the turbulence is inhomogeneous and anisotropic. It is shown that the subgrid stress tensor (SGS) tensor, for the case where the filtering operation is performed in physical space and applied in the inhomogeneous flow directions, contains two components: a rapid
Physics of Fluids, 2009
The velocity increment (VI) model, which was introduced by Brun et al., is improved by employing ... more The velocity increment (VI) model, which was introduced by Brun et al., is improved by employing the Kolmogorov equation of filtered velocity in this paper. This model has two different formulations: a dynamic formulation and a simplified constant form in high Reynolds number turbulence. A priori tests in isotropic turbulence and wall-bounded turbulence are performed. A posteriori tests of decaying turbulence and channel Poiseuille flow are made to testify the model performance, especially on the energy backscatter. The simple constant coefficient formulation has good performance, and avoids the ensemble average operation, which exists in other subgrid models. This constant improved VI model is particularly proposed in complicated large-eddy simulation projects.
Journal of Fluid Mechanics, 2007
A new subgrid eddy-viscosity model is proposed in this paper. Full details of the derivation of t... more A new subgrid eddy-viscosity model is proposed in this paper. Full details of the derivation of the model are given with the assumption of homogeneous turbulence. The formulation of the model is based on the dynamic equation of the structure function of resolved scale turbulence. By means of the local volume average, the effect of the anisotropy is taken into account in the generalized Kolmogorov equation, which represents the equilibrium energy transfer in the inertial subrange. Since the proposed model is formulated directly from the filtered Navier–Stokes equation, the resulting subgrid eddy viscosity has the feature that it can be adopted in various turbulent flows without any adjustments of model coefficient. The proposed model predicts the major statistical properties of rotating turbulence perfectly at fairly low-turbulence Rossby numbers whereas subgrid models, which do not consider anisotropic effects in turbulence energy transfer, cannot predict this typical anisotropic tu...
Acta Mechanica Sinica, 2014
Eddy-damping quasinormal Markovian (EDQNM) theory is employed to calculate the resolved-scale spe... more Eddy-damping quasinormal Markovian (EDQNM) theory is employed to calculate the resolved-scale spectrum and transfer spectrum, based on which we investigate the resolved-scale scaling law. Results show that the scaling law of the resolved-scale turbulence, which is affected by several factors, is far from that of the full-scale turbulence and should be corrected. These results are then applied to an existing subgrid model to improve its performance. A series of simulations are performed to verify the necessity of a fixed scaling law in the subgrid modeling. Keywords Scaling law • Large-eddy simulation • CZZS model 1 Introduction Kolmogorov introduced the 2/3 scaling law for the secondorder structure function in isotropic turbulence, which is
Journal of Thermal Science, 2007
Large-eddy simulation developments and validations are presented for an improved simulation of tu... more Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria: numerical qualities (precision and spectral characteristics), and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and "low-cost" shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2015
The present study carried out a pure large eddy simulation (LES) on a NACA65 linear compressor ca... more The present study carried out a pure large eddy simulation (LES) on a NACA65 linear compressor cascade (chord-based Reynolds number: 382 000), at an incidence angle of 4°. In this configuration, a corner separation at the juncture of the blade suction side and the end-wall is clearly observed experimentally. For the simulation, 852 CPUs are used in parallel and particular attention is paid to the inflow conditions, coupling LES with the calculation of the inlet boundary layer and associated velocity fluctuations. The shear-improved Smagorinsky model, which has been proved to be competent for turbomachines, is used in this study. Numerical results are carefully compared with pressure measurements, two-dimensional and stereo particle image velocimetry. LES is found to be superior to Reynolds-averaged Navier–Stokes approach in predicting the three-dimensional separated flows in the compressor cascade since pressure coefficients and losses are in very good agreement with the experiment....
Physics of Fluids, 1999
Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer ... more Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer flows at high Reynolds number with mean wall shear stress boundary condition
Physics of Fluids, 1999
Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer ... more Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer flows at high Reynolds number with mean wall shear stress boundary condition
Physics of Fluids, 1999
Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer ... more Articles you may be interested in Large eddy simulations of turbulent channel and boundary layer flows at high Reynolds number with mean wall shear stress boundary condition
Journal of Fluid Mechanics, 2007
A shear-improved Smagorinsky model is introduced based on results concerning mean-shear effects i... more A shear-improved Smagorinsky model is introduced based on results concerning mean-shear effects in wall-bounded turbulence. The Smagorinsky eddy-viscosity is modified asvT=(Csδ)2(|S|—|〈S〉|): the magnitude of the mean shear |〈S〉|is subtracted from the magnitude of the instantaneous resolved rate-of-strain tensor |S|;CSis the standard Smagorinsky constant and Δ denotes the grid spacing. This subgrid-scale model is tested in large-eddy simulations of plane-channel flows at Reynolds numbersReτ= 395 andReτ= 590. First comparisons with the dynamic Smagorinsky model and direct numerical simulations for mean velocity, turbulent kinetic energy and Reynolds stress profiles, are shown to be extremely satisfactory. The proposed model, in addition to being physically sound and consistent with the scale-by-scale energy budget of locally homogeneous shear turbulence, has a low computational cost and possesses a high potential for generalization to complex non-homogeneous turbulent flows.
Springer Proceedings in Physics
Abstract. The aim of the study is to compare the LES of corner separation, considered as a refere... more Abstract. The aim of the study is to compare the LES of corner separation, considered as a reference, in the LMFA-NACA65 linear compressor cascade to RANS simulations using Wilcox two-equation models (k − ω). The LES was carried-out by Gao et al. [1] using the Shearimproved Smagorinsky model (SISM), and has been validated by comparison with the experimental data obtained by Ma et al. [2]. Two steady RANS simulations are carried out using k− ω models: Wilcox 1988 model and Wilcox 1988 model with quadratic constitutive relation. First, the analysis will consider the total pressure losses on a two-dimensional section downstream of the cascade. The Reynolds stresses and the turbulent kinetic energy budget are analysed within the separation region, on a two-dimensional section at the trailing edge of the blade. The RANS simulations mostly overestimate the total pressure losses and the size of the corner separation, compared to the LES and the experiment. The RANS simulations also overest...
Direct and Large-Eddy Simulation VII
ABSTRACT The velocity increment (VI) model of Brun et al. is improved by employing the Kolmogorov... more ABSTRACT The velocity increment (VI) model of Brun et al. is improved by employing the Kolmogorov equation of filtered velocity (KEF). The dynamic model coefficient is derived. In high Reynolds number turbulence, it is simplified in a constant form. A priori and a posteriori tests are made to testify the model performance. The constant coefficient form is low-cost and recommended.
12th European Conference on Turbomachinery Fluid Dynamics and hermodynamics
This study aims at analyzing the modeling of turbulence in a tip-leakage flow. The academic confi... more This study aims at analyzing the modeling of turbulence in a tip-leakage flow. The academic configuration considered is made of a single airfoil and a flat casing, with clearance, at Re=9.3e5. For characterising the turbulence, a zonal large-eddy simulation (ZLES), validated against experimental data, is considered as reference. ZLES was previously shown to describe precisely the flow features in the tip region, including the Reynolds stresses. Two steady Reynolds-averaged Navier-Stokes (RANS) simulations, using Wilcox's k-ω model, are evaluated against this reference. The first simulation uses the Boussinesq constitutive relation, whereas the second simulation relies on the quadratic constitutive relation (QCR). The analysis focuses on the mean velocities, the Reynolds stresses and a term-to-term decomposition of the turbulent kinetic energy budget. RANS is shown to underestimate the vorticity of the flow, the Reynolds stresses and the turbulent kinetic energy budget terms. The QCR has little effects on these deficits. KEYWORDS TIP-LEAKAGE FLOW, SINGLE AIRFOIL, RANS, LES, REYNOLDS STRESSES, TURBULENT KINETIC ENERGY BUDGET NOMENCLATURE M Mach number ∆x + , ∆y + , ∆z + Cell sizes at the wall, in wall O Normalized rotation tensor units Re c Reynolds number based on Π Sub-grid scale stress tensor the chord length of the blade Ξ Numerical residual tensor U Free-stream velocity δ ij Kroeneker symbol c Chord-length of the blade ρ Density h Tip-clearance height τ Viscous stress tensor k Turbulent kinetic energy τ t \τ QCR t Reynolds stress tensor with p Pressure Boussinesq constitutive u 1 , u 2 , u 3 Stream-wise (resp. transverse relation \with QCR and span-wise) velocities ω Turbulent kinetic energy x 1 , x 2 , x 3 Stream-wise (resp. transverse specific dissipation rate and span-wise) directions
Computers & Fluids
The generation of turbulent inflow conditions in large-eddy simulation (LES) is a key ingredient ... more The generation of turbulent inflow conditions in large-eddy simulation (LES) is a key ingredient for general applications of LES in both academic turbulent flows and industrial designs with complicated engineering flows. This is because accurate predictions of the fluid behaviour are strongly dependent on the inflow conditions, particularly in turbulent flows at high turbulent Reynolds numbers. This paper aims at improving the vortex method (VM) of Sergent [1] that demands long adaptive distances (12 times the half channel height, for a channel flow at Re τ = 395) to achieve high quality turbulence, and evaluating the equilibrium of the flow field obtained in terms of both the equilibrium of the mean flow and that of the turbulence (inter-scale turbulent energy transfer). The mean flow equilibrium is checked with classic criteria such as the friction velocity. In order to assess the equilibrium of turbulence, we propose using the velocity-derivative skewness, because it associates with the balance of energy transfer between large-and small-scale fluid motions. Numerical tests with the optimised set of model parameters reveal that the IVM is very efficient, in terms of adaptive distance, in generating high-quality synthetic turbulent fluctuations over a moderate distance: 6h for channel flow and 21δ for flat-plate boundary layer, with h and δ being respectively the half channel height and the nominal boundary layer thickness.
Http Www Theses Fr, 1992
Le travail de cette these est une contribution a l'etude de la turbulence inhomogene et s'... more Le travail de cette these est une contribution a l'etude de la turbulence inhomogene et s'inscrit dans le cadre d'etude a finalite aeronautique. Il s'agit d'une approche, par simulation numerique directe des grandes echelles de la turbulence, de l'interaction de deux turbulences d'echelles et de niveaux energetiques differents, placees cote a cote a l'instant initial et evoluant librement sans gradient de vitesse moyenne. Une telle situation physique constitue le cas le plus simple pour l'etude des phenomenes de transport spatial de turbulence, une seule direction d'inhomogeneite etant presente. Le but essentiel de l'etude est de completer les resultats experimentaux fournis par un travail effectue par Warhaft a l'universite de Cornell, contribuant par la a une meilleure comprehension de mecanismes physiques encore mal pris en compte dans les modeles simples. Les resultats de simulation montrent un bon accord qualitatif avec l'experience existante. De plus, des informations non accessibles experimentalement sont obtenues. Ce sont les correlations triples de vitesse qui assurent le transport de turbulence, tandis que la correlation pression vitesse tend a contrebalancer legerement ce transport. Le mecanisme de transport de turbulence est maintenant mieux compris, notamment en ce qui concerne le role joue par l'intermittence. Dans un but pratique d'applications industrielles, les resultats de simulation sont compares a ceux obtenus dans la meme situation par des modeles de turbulence simples (modeles en un point). Les comparaisons montrent que les modeles classiques ne prennent pas en compte le mecanisme de l'intermittence. Une modification des modeles classiques est introduite et les resultats se trouvent ameliores. L’etude a ensuite ete etendue au cas ou la couche de melange turbulente est soumise a une rotation en bloc. Les resultats montrent que la force de Coriolis modifie de facon considerable le mecanisme de transport. Deux effets sont identifies; les correlations triples sont fortement inhibees; la correlation pression vitesse assure le transport. Le premier effet a ete modelise; tandis que la prise en compte du second effet dans les modeles simples reste un probleme ouvert
ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C, 2010
In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anis... more In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anisotropy affect the subgrid stress via the mean flow gradient. A method of evaluating the mean effects is to split the subgrid stress tensor into “rapid” and “slow” parts. This decomposition was introduced by Shao et al. (1999) and applied to A Priori tests of existing subgrid models in the case of a turbulent mixing layer. In the present work, the decomposition is extended to the case of a passive scalar in inhomogeneous turbulence. The contributions of rapid and slow subgrid scalar flux, both in the equations of scalar variance and scalar flux, are analyzed. A Priori numerical tests are performed in a turbulent Couette flow with a mean scalar gradient. Results are then used to evaluate the performances of different popular subgrid scalar models. It is shown that existing models can not well simulate the slow part and need to be improved. In order to improve the modeling, an extension of ...
Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 1998
The present study sheds light on the subgrid modeling problem encountered in large eddy simulatio... more The present study sheds light on the subgrid modeling problem encountered in large eddy simulation (LES) of practical flows where the turbulence is inhomogeneous and anisotropic. It is shown that the subgrid stress tensor (SGS) tensor, for the case where the filtering operation is performed in physical space and applied in the inhomogeneous flow directions, contains two components: a rapid