A. Toutant - Academia.edu (original) (raw)

Papers by A. Toutant

Research paper thumbnail of Analysis and modeling of bubble-induced agitation from direct numerical simulation of homogeneous bubbly flows

Research paper thumbnail of Interaction

between a deformable buoyant bubble and a homogeneous isotropic turbulence

Research paper thumbnail of Influence of discharge and jet flow coupling on atmospheric pressure plasma homogeneity

Journal of Physics D: Applied Physics, 2015

ABSTRACT

Research paper thumbnail of Modélisation physique des interactions entre interfaces et turbulence

Turbulent two-phase flows abound in nature and engineering applications. The complex interactions... more Turbulent two-phase flows abound in nature and engineering applications. The complex interactions between interfaces and turbulence strongly impact the flow properties. Consequently, there is both a scientific and industrial interest to study this two-way coupling phenomenon. Local measurements, e.g. deformations of interfaces, are very difficult and the only tools able to provide information are numerical experiments. Unfortunately, Direct Numerical Simulations (DNS) have to entail a number of degrees of freedom proportional to the third power of the Reynolds number to correctly describe the flow behavior. This extremely hard constraint makes it impossible to use DNS for industrial applications. In order to successfully carry out industrial simulations their numerical cost has to be reduced. In brief, we have improved a mixed front-tracking/VOF method in order to simulate accurately interactions between interfaces and turbulence. Thanks to reliable DNS, we study this twoway coupling phenomenon in the purpose of developing the ISS concept, an equivalent to Abstract v LES for two-phase flows. Further work concerns implementation and a posteriori tests of the developed models. We hope that ISS will be able to simulate (at a low cost, around 2 or 3 times less of degrees of freedom by direction than DNS) turbulent two-phase flows with many bubbles or droplets at high Reynolds numbers. Πoµϕóλνξò e ανθρωπoς Homo bulla

Research paper thumbnail of Effects of Turbulence on Interfacial Heat Transfer: A Priori Test and Filters Evaluation

Research paper thumbnail of Jump conditions for filtered quantities at an under-resolved discontinuous interface. Part 1: Theoretical development

International Journal of Multiphase Flow, 2009

Research paper thumbnail of Towards large eddy simulation of isothermal two-phase flows: Governing equations and a priori tests

International Journal of Multiphase Flow, 2007

This article reports on the potential of application of LES in the calculation of turbulent two-p... more This article reports on the potential of application of LES in the calculation of turbulent two-phase flows, in the case where each phase is resolved and interfaces remain much larger than the mesh size. In comparison with single-phase flow, successful application of LES to resolve two-phase flow problems should account for the complex interaction between turbulence and interfaces. Non-linear transfers of turbulent energy across the interface have to be accurately modeled. The derivation of the complete filtered two-phase flow governing equations has been formulated to deal with turbulence at the interface in a comprehensive and practical way. Explicit filtering of 2D direct numerical simulations has been employed to evaluate the order of magnitude of the new subgrid contributions. A parametric study on the academic test case of two counter-rotative vortices and a more complex test case of phase inversion in a closed box have been utilized to perform an order of magnitude analysis of different transport mechanisms. Important features of turbulent energy transfer across the interface have been discussed. Analyses of the numerical results have been conducted to derive conclusions on the relative importance of the different subgrid scale contributions, and modeling issues and solutions are provided.

Research paper thumbnail of Numerical Study of Turbulent Confined Jets Impinging on a Heated Substrate for Thin Film Deposition

Journal of Fluids Engineering, 2014

This paper reports on the study of confined jets and jets interaction in terms of increasing chem... more This paper reports on the study of confined jets and jets interaction in terms of increasing chemical transport. The context of this study is the atmospheric pressure plasma-enhanced chemical vapor deposition, higher thin film growth rate being desired, while maintaining total flow rate as low as possible. Turbulence mixing and enhanced heat transfer are the physical mechanisms identified as being capable of increasing the growth rate at atmospheric pressure. A numerical study of jets impinging on a heated substrate was carried out using quasicompressible Reynolds-Averaged Navier–Stokes (RANS) equations. Abe–Kondoh–Nagano (AKN) low-Reynolds k-ε and standard k-ε models were tested using an unconfined impinging jet at Reynolds number Re = 23,750 for jet diameter to plate-spacing ratios of H/d = 2 and H/d = 6. Results were compared with experimental data from the literature. Based on numerical results and in accordance with existing findings, the AKN low-Reynolds k-ε was shown to be re...

Research paper thumbnail of DNS of the interaction between a deformable buoyant bubble and a spatially decaying turbulence: A priori tests for LES two-phase flow modelling

Computers & Fluids, 2008

This paper reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly deformable ... more This paper reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly deformable bubble in a spatially decaying turbulence. The complex interaction between interface and turbulence is fully resolved. This two-way coupling phenomenon is found to be of great importance for the flow dynamic. An explicit filtering of the simulation has been employed to evaluate the order of magnitude of the specific subgrid contributions in the Large Eddy Simulation (LES) modelling case. Subgrid closure models are proposed and evaluated thanks to a priori tests.

Research paper thumbnail of Interface–turbulence interaction

Research paper thumbnail of Interaction between a deformable buoyant bubble and a homogeneous isotropic turbulence

This communication reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly def... more This communication reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly deformable bubble in isotropic turbulent flows. The complex interaction between interface and turbulence is fully resolved. This two-way coupling phenomenon is found to be of great importance for the flow dynamic. An explicit filtering of the simulation has been employed to evaluate the order of magnitude of the specific subgrid contributions in the Large Eddy Simulation (LES) modelling case. Closure models are proposed.

Research paper thumbnail of Numerical simulation of phase separation and a priori two-phase LES filtering

Computers & Fluids, 2008

This work reports on the potential application of Large Eddy Simulation (LES) in the calculation ... more This work reports on the potential application of Large Eddy Simulation (LES) in the calculation of turbulent isothermal two-phase flows, in the case where the large scales of each phase are resolved and small interface structures can be smaller than the mesh size. In comparison with single phase flows, application of LES to two-phase flow problems should account for the complex interaction between the interface and the turbulent motion. The complete filtered two-phase flow equations are formulated to deal with turbulence at the interface. Explicit filtering of 3D direct numerical simulations of a phase separation problem has been employed to evaluate the order of magnitude of the specific subgrid contributions. Analyses of the numerical results have been conducted to derive conclusions on the relative importance of the different subgrid scale contributions. Modeling issues and turbulent energy transfer across the interface are discussed.

Research paper thumbnail of Etude Des Transferts Thermiques Au Sein D'Un Lit De Particules Contenant Un Materiau a Changement De Phase Pour Le Stockage De Chaleur

AA-CAES (Advanced Adiabatic Compressed Air Energy Storage) is a process which aims to store elect... more AA-CAES (Advanced Adiabatic Compressed Air Energy Storage) is a process which aims to store electricity by compressing ambient air. The heat produced can be stored in particle beds (packed or fluidized) made of Phase Change Material (PCM) which will modify the heat transfer throughout the whole bed compared with solid particle beds. One phenomenon involved is the natural convection occurring when the PCM is in liquid phase, whose effect was investigated by simulating an isolated particle in liquid phase in the OpenFOAM software. A correlation between the Nusselt and Prandtl and Rayleigh numbers was established and validated by comparison of the predicted temporal 23 ème Congrès Français de Mécanique Lille, 28 Août au 1 er Septembre 2017 2 evolution of the mean temperature of the particle with the profiles obtained in the OpenFOAM simulations for different (Rayleigh, Prandtl) values. Mots clefs : Transferts thermiques ; Convection naturelle ; Matériaux à Changement de Phase ; CFD Cha...

Research paper thumbnail of Thermal Boundary Condition Influence on Bi-Periodic Channel Flow with High Thermal Gradient

Machine Dynamics Research, 2011

Research paper thumbnail of Gas-Solid Flow in a Fluidized-Particle Tubular Solar Receiver: Off-Sun Experimental Flow Regimes Characterization

Energies

The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for h... more The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for heating particles at high temperature in the context of the next generation of solar power tower. Similar to most existing central solar receivers, the irradiated part of the system, the absorber, is composed of tubes in which circulate the fluidized particles. In this concept, the bottom tip of the tubes is immersed in a fluidized bed generated in a vessel named the dispenser. A secondary air injection, called aeration, is added at the bottom of the tube to stabilize the flow. Contrary to risers, the particle mass flow rate is controlled by a combination of the overpressure in the dispenser and the aeration air velocity in the tube. This is an originality of the system that justifies a specific study of the fluidization regimes in a wide range of operating parameters. Moreover, due to the high value of the aspect ratio, the particle flow structure varies along the tube. Experiments were ...

Research paper thumbnail of Direct simulations and subgrid modeling of turbulent channel flows asymmetrically heated from both walls

Physics of Fluids

Thermal large-eddy simulations (T-LES) and a direct numerical simulation are carried out in a bi-... more Thermal large-eddy simulations (T-LES) and a direct numerical simulation are carried out in a bi-periodical channel with hot and cold wall temperatures of, respectively, 900 and 1300 K. The mean fluid temperature is lowered below the cold wall temperature thanks to a heat source, resulting in a both walls heating of the fluid. The hot and cold wall friction Reynolds numbers are, respectively, 640 and 1000. These conditions are representative of the working conditions of gas-pressurized solar receiver of solar power tower. The low Mach number Navier–Stokes equations are solved. The coupling between the dynamic and the temperature effects is considered. In the T-LES, both the momentum convection and the density–velocity correlation subgrid terms are modeled. Functional models, structural models, and mixed models are considered. A tensorial version of the anisotropic minimum-dissipation (AMD) model is also investigated. The Quick and the second-order-centered schemes are tested for the discretization of the mass convection term. First, an overview of the results of 17 T-LES on first- and second-order statistics is proposed. It permits selecting 6 of these simulations for a detailed analysis consisting in the investigation of profiles of mean quantities and turbulent correlations. Particular attention is given to the wall heat fluxes because they are a critical point for the design and the optimization of solar receivers. Overall, the first-order statistics are better predicted than the second-order's. The tensorial AMD model takes advantage of the classical AMD model properties and better reproduces the anisotropy of the flow thanks to its formulation. The tensorial AMD model produces the most reliable and efficient results among the considered models.

Research paper thumbnail of A priori tests of subgrid-scale models in an anisothermal turbulent channel flow at low mach number

International Journal of Thermal Sciences

The subgrid-scale modelling of a low Mach number strongly anisothermal turbulent flow is investig... more The subgrid-scale modelling of a low Mach number strongly anisothermal turbulent flow is investigated using direct numerical simulations. The study is based on the filtering of the low Mach number equations, suited to low Mach number flows with highly variable fluid properties. The results are relevant to formulations of the filtered low Mach number equations established with the classical filter or the Favre filter. The two most significant subgrid terms of the filtered low Mach number equations are considered. They are associated with the momentum convection and the densityvelocity correlation. We focus on eddy-viscosity and eddy-diffusivity models. Subgridscale models from the literature are analysed and two new models are proposed. The subgrid-scale models are compared to the exact subgrid term using the instantaneous flow field of the direct numerical simulation of a strongly anisothermal fully developed turbulent channel flow. There is no significant differences between the use of the classical and Favre filter regarding the performance of the models. We suggest that the models should take into account the asymptotic near-wall behaviour of the filter length. Eddy-viscosity and eddy-diffusivity models are able to represent the energetic contribution of the subgrid term but not its effect in the flow governing equations. The AMD and scalar AMD models are found to be in better agreement with the exact subgrid terms than the other investigated models in the a priori tests.

Research paper thumbnail of Numerical simulations of unsteady viscous incompressible flows using general pressure equation

Journal of Computational Physics

In fluid dynamics, an important problem is linked to the knowledge of the fluid pressure. Recentl... more In fluid dynamics, an important problem is linked to the knowledge of the fluid pressure. Recently, another approach to study incompressible fluid flow was suggested. It consists in using a general pressure equation (GPE) derived from compressible Navier-Stokes equation. In this paper, GPE is considered and compared with the Chorin's artificial compressibility method (ACM) and the Entropically damped artificial compressibility (EDAC) method. The three methods are discretized in a staggered grid system with second order centered schemes in space and a third order Runge-Kutta scheme in time. Three test cases are realized: twodimensional Taylor-Green vortex flow, the traveling wave and the doubly periodic shear layers. It is demonstrated that GPE is accurate and efficient to capture the correct behavior for unsteady incompressible flows. The numerical results obtained by GPE are in excellent agreement with those obtained by ACM, EDAC and a classical finite volume method with a Poisson equation. Furthermore, GPE convergence is better than ACM convergence. The proposed general pressure equation (GPE) allows to solve general, time-accurate , incompressible Navier-Stokes flows. Finally, the parametric study realized in terms of Mach and Prandtl numbers shows that the velocity divergence can be limited by an arbitrary maximum and that acoustic waves can be damped.

Research paper thumbnail of General and exact pressure evolution equation

Physics Letters A

A crucial issue in fluid dynamics is related to the knowledge of the fluid pressure. A new genera... more A crucial issue in fluid dynamics is related to the knowledge of the fluid pressure. A new general pressure equation is derived from compressible Navier-Stokes equation. This new pressure equation is valid for all real dense fluids for which the pressure tensor is isotropic. It is argued that this new pressure equation allows unifying compressible, low-Mach and incompressible approaches. Moreover, this equation should be able to replace the Poisson equation in isothermal incompressible fluids. For computational fluid dynamics, it can be seen as an alternative to Lattice Boltzmann methods and as the physical justification of artificial compressibility. ∂ i ∂ i P = −(∂ j u i)(∂ i u j) (2)

Research paper thumbnail of Investigation of thermal large-eddy simulation approaches in a highly turbulent channel flow submitted to strong asymmetric heating

Physics of Fluids

This study deals with thermal large-eddy simulation (T-LES) of anisothermal turbulent channel flo... more This study deals with thermal large-eddy simulation (T-LES) of anisothermal turbulent channel flow in the working conditions of solar receivers used in concentrated solar power towers. The flow is characterized by high-temperature levels and strong heat fluxes. The hot and cold friction Reynolds numbers of the simulations are, respectively, 630 and 970. The Navier–Stokes equations are solved under the low-Mach number approximation and the thermal dilatation is taken into account. The momentum convection and the density–velocity correlation subgrid terms are modeled. Functional, structural, and mixed subgrid-scale models are investigated. A tensorial version of the classical anisotropic minimum-dissipation (AMD) model is studied and produces good results. A Quick scheme and a second-order-centered scheme are tested for the discretization of the mass convection term. First, a global assessment of 22 large-eddy simulations is proposed, then six are selected for a careful analysis including profiles of mean quantities and fluctuation values as well as a comparison of instantaneous fields. Probability density functions of wall heat fluxes are plotted. The results point out that T-LESs performed with the Quick scheme tend to underestimate the wall heat flux whereas the second-order-centered scheme significantly improves its estimation. T-LESs tend to overestimate the peaks of velocity correlations. When regarding the dimensionless profiles of fluctuations, the tensorial AMD model provides better results than the other assessed models. For the heat flux estimation, the best agreement is found with the AMD model combined with the second-order-centered scheme.

Research paper thumbnail of Analysis and modeling of bubble-induced agitation from direct numerical simulation of homogeneous bubbly flows

Research paper thumbnail of Interaction

between a deformable buoyant bubble and a homogeneous isotropic turbulence

Research paper thumbnail of Influence of discharge and jet flow coupling on atmospheric pressure plasma homogeneity

Journal of Physics D: Applied Physics, 2015

ABSTRACT

Research paper thumbnail of Modélisation physique des interactions entre interfaces et turbulence

Turbulent two-phase flows abound in nature and engineering applications. The complex interactions... more Turbulent two-phase flows abound in nature and engineering applications. The complex interactions between interfaces and turbulence strongly impact the flow properties. Consequently, there is both a scientific and industrial interest to study this two-way coupling phenomenon. Local measurements, e.g. deformations of interfaces, are very difficult and the only tools able to provide information are numerical experiments. Unfortunately, Direct Numerical Simulations (DNS) have to entail a number of degrees of freedom proportional to the third power of the Reynolds number to correctly describe the flow behavior. This extremely hard constraint makes it impossible to use DNS for industrial applications. In order to successfully carry out industrial simulations their numerical cost has to be reduced. In brief, we have improved a mixed front-tracking/VOF method in order to simulate accurately interactions between interfaces and turbulence. Thanks to reliable DNS, we study this twoway coupling phenomenon in the purpose of developing the ISS concept, an equivalent to Abstract v LES for two-phase flows. Further work concerns implementation and a posteriori tests of the developed models. We hope that ISS will be able to simulate (at a low cost, around 2 or 3 times less of degrees of freedom by direction than DNS) turbulent two-phase flows with many bubbles or droplets at high Reynolds numbers. Πoµϕóλνξò e ανθρωπoς Homo bulla

Research paper thumbnail of Effects of Turbulence on Interfacial Heat Transfer: A Priori Test and Filters Evaluation

Research paper thumbnail of Jump conditions for filtered quantities at an under-resolved discontinuous interface. Part 1: Theoretical development

International Journal of Multiphase Flow, 2009

Research paper thumbnail of Towards large eddy simulation of isothermal two-phase flows: Governing equations and a priori tests

International Journal of Multiphase Flow, 2007

This article reports on the potential of application of LES in the calculation of turbulent two-p... more This article reports on the potential of application of LES in the calculation of turbulent two-phase flows, in the case where each phase is resolved and interfaces remain much larger than the mesh size. In comparison with single-phase flow, successful application of LES to resolve two-phase flow problems should account for the complex interaction between turbulence and interfaces. Non-linear transfers of turbulent energy across the interface have to be accurately modeled. The derivation of the complete filtered two-phase flow governing equations has been formulated to deal with turbulence at the interface in a comprehensive and practical way. Explicit filtering of 2D direct numerical simulations has been employed to evaluate the order of magnitude of the new subgrid contributions. A parametric study on the academic test case of two counter-rotative vortices and a more complex test case of phase inversion in a closed box have been utilized to perform an order of magnitude analysis of different transport mechanisms. Important features of turbulent energy transfer across the interface have been discussed. Analyses of the numerical results have been conducted to derive conclusions on the relative importance of the different subgrid scale contributions, and modeling issues and solutions are provided.

Research paper thumbnail of Numerical Study of Turbulent Confined Jets Impinging on a Heated Substrate for Thin Film Deposition

Journal of Fluids Engineering, 2014

This paper reports on the study of confined jets and jets interaction in terms of increasing chem... more This paper reports on the study of confined jets and jets interaction in terms of increasing chemical transport. The context of this study is the atmospheric pressure plasma-enhanced chemical vapor deposition, higher thin film growth rate being desired, while maintaining total flow rate as low as possible. Turbulence mixing and enhanced heat transfer are the physical mechanisms identified as being capable of increasing the growth rate at atmospheric pressure. A numerical study of jets impinging on a heated substrate was carried out using quasicompressible Reynolds-Averaged Navier–Stokes (RANS) equations. Abe–Kondoh–Nagano (AKN) low-Reynolds k-ε and standard k-ε models were tested using an unconfined impinging jet at Reynolds number Re = 23,750 for jet diameter to plate-spacing ratios of H/d = 2 and H/d = 6. Results were compared with experimental data from the literature. Based on numerical results and in accordance with existing findings, the AKN low-Reynolds k-ε was shown to be re...

Research paper thumbnail of DNS of the interaction between a deformable buoyant bubble and a spatially decaying turbulence: A priori tests for LES two-phase flow modelling

Computers & Fluids, 2008

This paper reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly deformable ... more This paper reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly deformable bubble in a spatially decaying turbulence. The complex interaction between interface and turbulence is fully resolved. This two-way coupling phenomenon is found to be of great importance for the flow dynamic. An explicit filtering of the simulation has been employed to evaluate the order of magnitude of the specific subgrid contributions in the Large Eddy Simulation (LES) modelling case. Subgrid closure models are proposed and evaluated thanks to a priori tests.

Research paper thumbnail of Interface–turbulence interaction

Research paper thumbnail of Interaction between a deformable buoyant bubble and a homogeneous isotropic turbulence

This communication reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly def... more This communication reports on results of a 3D Direct Numerical Simulation (DNS) of a strongly deformable bubble in isotropic turbulent flows. The complex interaction between interface and turbulence is fully resolved. This two-way coupling phenomenon is found to be of great importance for the flow dynamic. An explicit filtering of the simulation has been employed to evaluate the order of magnitude of the specific subgrid contributions in the Large Eddy Simulation (LES) modelling case. Closure models are proposed.

Research paper thumbnail of Numerical simulation of phase separation and a priori two-phase LES filtering

Computers & Fluids, 2008

This work reports on the potential application of Large Eddy Simulation (LES) in the calculation ... more This work reports on the potential application of Large Eddy Simulation (LES) in the calculation of turbulent isothermal two-phase flows, in the case where the large scales of each phase are resolved and small interface structures can be smaller than the mesh size. In comparison with single phase flows, application of LES to two-phase flow problems should account for the complex interaction between the interface and the turbulent motion. The complete filtered two-phase flow equations are formulated to deal with turbulence at the interface. Explicit filtering of 3D direct numerical simulations of a phase separation problem has been employed to evaluate the order of magnitude of the specific subgrid contributions. Analyses of the numerical results have been conducted to derive conclusions on the relative importance of the different subgrid scale contributions. Modeling issues and turbulent energy transfer across the interface are discussed.

Research paper thumbnail of Etude Des Transferts Thermiques Au Sein D'Un Lit De Particules Contenant Un Materiau a Changement De Phase Pour Le Stockage De Chaleur

AA-CAES (Advanced Adiabatic Compressed Air Energy Storage) is a process which aims to store elect... more AA-CAES (Advanced Adiabatic Compressed Air Energy Storage) is a process which aims to store electricity by compressing ambient air. The heat produced can be stored in particle beds (packed or fluidized) made of Phase Change Material (PCM) which will modify the heat transfer throughout the whole bed compared with solid particle beds. One phenomenon involved is the natural convection occurring when the PCM is in liquid phase, whose effect was investigated by simulating an isolated particle in liquid phase in the OpenFOAM software. A correlation between the Nusselt and Prandtl and Rayleigh numbers was established and validated by comparison of the predicted temporal 23 ème Congrès Français de Mécanique Lille, 28 Août au 1 er Septembre 2017 2 evolution of the mean temperature of the particle with the profiles obtained in the OpenFOAM simulations for different (Rayleigh, Prandtl) values. Mots clefs : Transferts thermiques ; Convection naturelle ; Matériaux à Changement de Phase ; CFD Cha...

Research paper thumbnail of Thermal Boundary Condition Influence on Bi-Periodic Channel Flow with High Thermal Gradient

Machine Dynamics Research, 2011

Research paper thumbnail of Gas-Solid Flow in a Fluidized-Particle Tubular Solar Receiver: Off-Sun Experimental Flow Regimes Characterization

Energies

The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for h... more The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for heating particles at high temperature in the context of the next generation of solar power tower. Similar to most existing central solar receivers, the irradiated part of the system, the absorber, is composed of tubes in which circulate the fluidized particles. In this concept, the bottom tip of the tubes is immersed in a fluidized bed generated in a vessel named the dispenser. A secondary air injection, called aeration, is added at the bottom of the tube to stabilize the flow. Contrary to risers, the particle mass flow rate is controlled by a combination of the overpressure in the dispenser and the aeration air velocity in the tube. This is an originality of the system that justifies a specific study of the fluidization regimes in a wide range of operating parameters. Moreover, due to the high value of the aspect ratio, the particle flow structure varies along the tube. Experiments were ...

Research paper thumbnail of Direct simulations and subgrid modeling of turbulent channel flows asymmetrically heated from both walls

Physics of Fluids

Thermal large-eddy simulations (T-LES) and a direct numerical simulation are carried out in a bi-... more Thermal large-eddy simulations (T-LES) and a direct numerical simulation are carried out in a bi-periodical channel with hot and cold wall temperatures of, respectively, 900 and 1300 K. The mean fluid temperature is lowered below the cold wall temperature thanks to a heat source, resulting in a both walls heating of the fluid. The hot and cold wall friction Reynolds numbers are, respectively, 640 and 1000. These conditions are representative of the working conditions of gas-pressurized solar receiver of solar power tower. The low Mach number Navier–Stokes equations are solved. The coupling between the dynamic and the temperature effects is considered. In the T-LES, both the momentum convection and the density–velocity correlation subgrid terms are modeled. Functional models, structural models, and mixed models are considered. A tensorial version of the anisotropic minimum-dissipation (AMD) model is also investigated. The Quick and the second-order-centered schemes are tested for the discretization of the mass convection term. First, an overview of the results of 17 T-LES on first- and second-order statistics is proposed. It permits selecting 6 of these simulations for a detailed analysis consisting in the investigation of profiles of mean quantities and turbulent correlations. Particular attention is given to the wall heat fluxes because they are a critical point for the design and the optimization of solar receivers. Overall, the first-order statistics are better predicted than the second-order's. The tensorial AMD model takes advantage of the classical AMD model properties and better reproduces the anisotropy of the flow thanks to its formulation. The tensorial AMD model produces the most reliable and efficient results among the considered models.

Research paper thumbnail of A priori tests of subgrid-scale models in an anisothermal turbulent channel flow at low mach number

International Journal of Thermal Sciences

The subgrid-scale modelling of a low Mach number strongly anisothermal turbulent flow is investig... more The subgrid-scale modelling of a low Mach number strongly anisothermal turbulent flow is investigated using direct numerical simulations. The study is based on the filtering of the low Mach number equations, suited to low Mach number flows with highly variable fluid properties. The results are relevant to formulations of the filtered low Mach number equations established with the classical filter or the Favre filter. The two most significant subgrid terms of the filtered low Mach number equations are considered. They are associated with the momentum convection and the densityvelocity correlation. We focus on eddy-viscosity and eddy-diffusivity models. Subgridscale models from the literature are analysed and two new models are proposed. The subgrid-scale models are compared to the exact subgrid term using the instantaneous flow field of the direct numerical simulation of a strongly anisothermal fully developed turbulent channel flow. There is no significant differences between the use of the classical and Favre filter regarding the performance of the models. We suggest that the models should take into account the asymptotic near-wall behaviour of the filter length. Eddy-viscosity and eddy-diffusivity models are able to represent the energetic contribution of the subgrid term but not its effect in the flow governing equations. The AMD and scalar AMD models are found to be in better agreement with the exact subgrid terms than the other investigated models in the a priori tests.

Research paper thumbnail of Numerical simulations of unsteady viscous incompressible flows using general pressure equation

Journal of Computational Physics

In fluid dynamics, an important problem is linked to the knowledge of the fluid pressure. Recentl... more In fluid dynamics, an important problem is linked to the knowledge of the fluid pressure. Recently, another approach to study incompressible fluid flow was suggested. It consists in using a general pressure equation (GPE) derived from compressible Navier-Stokes equation. In this paper, GPE is considered and compared with the Chorin's artificial compressibility method (ACM) and the Entropically damped artificial compressibility (EDAC) method. The three methods are discretized in a staggered grid system with second order centered schemes in space and a third order Runge-Kutta scheme in time. Three test cases are realized: twodimensional Taylor-Green vortex flow, the traveling wave and the doubly periodic shear layers. It is demonstrated that GPE is accurate and efficient to capture the correct behavior for unsteady incompressible flows. The numerical results obtained by GPE are in excellent agreement with those obtained by ACM, EDAC and a classical finite volume method with a Poisson equation. Furthermore, GPE convergence is better than ACM convergence. The proposed general pressure equation (GPE) allows to solve general, time-accurate , incompressible Navier-Stokes flows. Finally, the parametric study realized in terms of Mach and Prandtl numbers shows that the velocity divergence can be limited by an arbitrary maximum and that acoustic waves can be damped.

Research paper thumbnail of General and exact pressure evolution equation

Physics Letters A

A crucial issue in fluid dynamics is related to the knowledge of the fluid pressure. A new genera... more A crucial issue in fluid dynamics is related to the knowledge of the fluid pressure. A new general pressure equation is derived from compressible Navier-Stokes equation. This new pressure equation is valid for all real dense fluids for which the pressure tensor is isotropic. It is argued that this new pressure equation allows unifying compressible, low-Mach and incompressible approaches. Moreover, this equation should be able to replace the Poisson equation in isothermal incompressible fluids. For computational fluid dynamics, it can be seen as an alternative to Lattice Boltzmann methods and as the physical justification of artificial compressibility. ∂ i ∂ i P = −(∂ j u i)(∂ i u j) (2)

Research paper thumbnail of Investigation of thermal large-eddy simulation approaches in a highly turbulent channel flow submitted to strong asymmetric heating

Physics of Fluids

This study deals with thermal large-eddy simulation (T-LES) of anisothermal turbulent channel flo... more This study deals with thermal large-eddy simulation (T-LES) of anisothermal turbulent channel flow in the working conditions of solar receivers used in concentrated solar power towers. The flow is characterized by high-temperature levels and strong heat fluxes. The hot and cold friction Reynolds numbers of the simulations are, respectively, 630 and 970. The Navier–Stokes equations are solved under the low-Mach number approximation and the thermal dilatation is taken into account. The momentum convection and the density–velocity correlation subgrid terms are modeled. Functional, structural, and mixed subgrid-scale models are investigated. A tensorial version of the classical anisotropic minimum-dissipation (AMD) model is studied and produces good results. A Quick scheme and a second-order-centered scheme are tested for the discretization of the mass convection term. First, a global assessment of 22 large-eddy simulations is proposed, then six are selected for a careful analysis including profiles of mean quantities and fluctuation values as well as a comparison of instantaneous fields. Probability density functions of wall heat fluxes are plotted. The results point out that T-LESs performed with the Quick scheme tend to underestimate the wall heat flux whereas the second-order-centered scheme significantly improves its estimation. T-LESs tend to overestimate the peaks of velocity correlations. When regarding the dimensionless profiles of fluctuations, the tensorial AMD model provides better results than the other assessed models. For the heat flux estimation, the best agreement is found with the AMD model combined with the second-order-centered scheme.