O. Lebaigue | CEA - Academia.edu (original) (raw)

Papers by O. Lebaigue

La Houille Blanche, 1998

ABSTRACT This paper gives a short presentation of the FASTNET team preliminary conclusions. This ... more ABSTRACT This paper gives a short presentation of the FASTNET team preliminary conclusions. This team tried to define a scientific strategy aimed at developing thermal-hydraulics in the nuclear and on-nuclear industry fields. The reflections were mainly conducted as a three stage process: - the identification of industrial problems, whose better resolution rely on a knowledge improvement in thermalhydraulics, - a state-of the-art analysis, which led to identify the actual limitations (and their origin) for the different components of the thermal-hydraulics expertise (physical rnodeling, numerical simulation, instrumentation, analytical and validation experiments), - the proposition of a coherent strategy to develop expertise in all these fields of thermal-hydraulics. This paper is a summarized version of a more detailed progress report. The work is still in progress...

31st Thermophysics Conference, 1996

Multiphase Science and Technology, 2004

A generator shoots droplets onto a heated plate inclined with respect to the trajectory of the dr... more A generator shoots droplets onto a heated plate inclined with respect to the trajectory of the droplets. The droplets rebound and evaporate. Given the physical properties of the liquid, the velocity, the diameter and the temperature of the impacting droplet, as well as the inclination and the temperature of the plate, the numerical simulation should predict the diameter and the surface temperature of the droplet after rebound.

ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover acti... more ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover actinides from a multicomponent solution. Due to their later handling and use, actinide precipitates have to satisfy strict requirements. In nuclear environment where experiments are limited, simulation may be the only way to test different industrial configurations in order to adjust industrial campaigns. In this manuscript, the modelling of the tetravalent uranium oxalate precipitation in an unbaffled reactor is achieved using a hybrid multizonal/CFD model. The population balance is solved according to the moment method in a multizonal model entirely parameterised through computational fluid dynamics calculations based on large-eddy simulation (LES) and a sub-grid model of micromixing. The modelling is applied to show how the specificity of flow field in an unbaffled reactor can have a noticeable effect on the uranium oxalate properties.

Multiphase Science and Technology, 2004

The test case concerns the simulation of a fluid inclusion rising in another stagnant fluid. The ... more The test case concerns the simulation of a fluid inclusion rising in another stagnant fluid. The transient rise velocity, and the steadystate rise velocity and shape should be compared to the results obtained with an accurate numerical technique.

ABSTRACT A dynamic evaporating contact line model for perfectly wetting fluids is built. This mod... more ABSTRACT A dynamic evaporating contact line model for perfectly wetting fluids is built. This model includes the disjoining pressure, surface tension, recoil pressure, interface resistance and viscous stress. A numerical method is used to solve the set of equations, including the two-dimensional diffusion-convection heat transfer problem. We compute the macroscopic contact angle and the overall evaporation heat transfer up to a fixed macroscopic length scale and describe the governing phenomena. We found that the motion of the contact line can lead to a tremendous increase of the local heat flux.

Multiphase Science and Technology, 2004

This test case is primarily dedicated to check the ability of a numerical method to simulate cont... more This test case is primarily dedicated to check the ability of a numerical method to simulate contact line effects, in particular the contact line hysteresis. It consists in computing the conditions for which a twodimensional droplet sticks or slides on an inclined wall.

Multiphase Science and Technology, 2004

This test case describes the theoretical solutions of three simple free boundary problems: the co... more This test case describes the theoretical solutions of three simple free boundary problems: the collapse of a vapor bubble in a subcooled liquid, the initial stage of the growth of a vapor bubble in a superheated liquid, and finally, the thermally controlled growth of a vapor bubble. It is requested to compute the bubble radius as well as the interface temperature and speed of displacement.

La Houille Blanche, 2003

Physical and numerical modeling of a dynamic contact line with phase-change: A dynamic contact li... more Physical and numerical modeling of a dynamic contact line with phase-change: A dynamic contact line model is built, using a slip condition at small scale. This model includes heat transfer in the solid and the liquid, recoil pressure and interface resistance. The effect of contact line displacement and phase change on the contact angle and the heat flux is studied. Different regimes are investigated, depending on physical and geometrical parameters.

Transport in Porous Media, 1989

The macroscopic description of the dynamics of two immiscible fluids flowing through a deformable... more The macroscopic description of the dynamics of two immiscible fluids flowing through a deformable porous medium is obtained from the description of the pore scale using the homogenization theory of periodic structures. The result is a generalization of the description of saturated porous media with a BIOT structure. The homogenization process permits the complete determination of the effective parameters and the clarification of the couplings between the different phases. Two simple examples are presented for the generalized Darcy flows. Special care is taken concerning the significance of the volume averaged stress, as provided by the homogenization process. It is shown that the physical stress is different from the volume averaged stress.

International Journal of Engineering Science, 1989

International Journal for Numerical Methods in Fluids, 2008

In the framework of numerical study of multiphase flows, different front-capturing methods are co... more In the framework of numerical study of multiphase flows, different front-capturing methods are compared. Two different approaches dealing with the incompressibility constraint will be compared, too. Then, every technique is tested on several relevant test cases in order to make a comparison. The surface tension treatment is evaluated for each method and every front-capturing method is tested on a case where turbulence is well developed. Finally, every method is studied through a phase inversion which is an unsteady and turbulent test-case.

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.

Computers & Fluids, 2012

ABSTRACT Among the various direct numerical simulation (DNS) methods dedicated to multiphase flow... more ABSTRACT Among the various direct numerical simulation (DNS) methods dedicated to multiphase flow, the front-tracking methods that use a Lagrangian mesh to describe explicitly the interfaces are generally considered as a very accurate and complex method. In this family of methods, while a fine Lagrangian mesh is desirable for a better representation of the interfacial area, the surface forces and the bubble or droplet volume, one cannot arbitrarily choose the Lagrangian mesh size. Indeed, the Lagrangian mesh displacement algorithm is unstable if the number of Lagrangian degrees of freedom does not match the number of involved Eulerian velocity points. As a consequence, in traditional front-tracking implementations, an accurate description of the interfaces is expensive in terms of Eulerian mesh cells. We demonstrate that a front-tracking interface smoothing (FTIS) method can reduce the constraints on the mesh sizes. It consists in damping the highest spatial frequency components of the Lagrangian mesh to compensate for the lack of Eulerian velocity points. The test case of fundamental proper frequency of a bubble proves the validity of the FTIS method. An example of a 3D-bubble rising shows the interest and the potential applications of the FTIS method.

Chemical Engineering Science, 2012

ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover acti... more ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover actinides from a multicomponent solution. Due to their later handling and use, actinide precipitates have to satisfy strict requirements. In nuclear environment where experiments are limited, simulation may be the only way to test different industrial configurations in order to adjust industrial campaigns. In this manuscript, the modelling of the tetravalent uranium oxalate precipitation in an unbaffled reactor is achieved using a hybrid multizonal/CFD model. The population balance is solved according to the moment method in a multizonal model entirely parameterised through computational fluid dynamics calculations based on large-eddy simulation (LES) and a sub-grid model of micromixing. The modelling is applied to show how the specificity of flow field in an unbaffled reactor can have a noticeable effect on the uranium oxalate properties.

Chemical Engineering Science, 2010

This article deals with the large-eddy simulation (LES) of a complex turbulent free-surface flow ... more This article deals with the large-eddy simulation (LES) of a complex turbulent free-surface flow in an unbaffled mixing tank reactor. The free-surface vortex generated in such a configuration is captured using a front-tracking method, while the stirrer is modelled with an immersed boundary condition technique. Comparisons of mean and fluctuating velocities show good agreement with both theory and experimental laser

This communication reports on the potential application of Large Eddy Simulation in the calculati... more This communication reports on the potential application of Large Eddy Simulation 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 lower 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 interface and turbulence. The complete filtered two-phase flow equations are formulated to deal with turbulence at the interface. Explicit filtering of 2D and 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.

Multiphase Science and Technology, 2004

The two-layer laminar Poiseuille flow is suggested as a case test. Two superimposed layers of vis... more The two-layer laminar Poiseuille flow is suggested as a case test. Two superimposed layers of viscous fluids separated by a flat interface are flowing in a horizontal channels. The analytical solution is provided.

La Houille Blanche, 1998

ABSTRACT This paper gives a short presentation of the FASTNET team preliminary conclusions. This ... more ABSTRACT This paper gives a short presentation of the FASTNET team preliminary conclusions. This team tried to define a scientific strategy aimed at developing thermal-hydraulics in the nuclear and on-nuclear industry fields. The reflections were mainly conducted as a three stage process: - the identification of industrial problems, whose better resolution rely on a knowledge improvement in thermalhydraulics, - a state-of the-art analysis, which led to identify the actual limitations (and their origin) for the different components of the thermal-hydraulics expertise (physical rnodeling, numerical simulation, instrumentation, analytical and validation experiments), - the proposition of a coherent strategy to develop expertise in all these fields of thermal-hydraulics. This paper is a summarized version of a more detailed progress report. The work is still in progress...

31st Thermophysics Conference, 1996

Multiphase Science and Technology, 2004

A generator shoots droplets onto a heated plate inclined with respect to the trajectory of the dr... more A generator shoots droplets onto a heated plate inclined with respect to the trajectory of the droplets. The droplets rebound and evaporate. Given the physical properties of the liquid, the velocity, the diameter and the temperature of the impacting droplet, as well as the inclination and the temperature of the plate, the numerical simulation should predict the diameter and the surface temperature of the droplet after rebound.

ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover acti... more ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover actinides from a multicomponent solution. Due to their later handling and use, actinide precipitates have to satisfy strict requirements. In nuclear environment where experiments are limited, simulation may be the only way to test different industrial configurations in order to adjust industrial campaigns. In this manuscript, the modelling of the tetravalent uranium oxalate precipitation in an unbaffled reactor is achieved using a hybrid multizonal/CFD model. The population balance is solved according to the moment method in a multizonal model entirely parameterised through computational fluid dynamics calculations based on large-eddy simulation (LES) and a sub-grid model of micromixing. The modelling is applied to show how the specificity of flow field in an unbaffled reactor can have a noticeable effect on the uranium oxalate properties.

Multiphase Science and Technology, 2004

The test case concerns the simulation of a fluid inclusion rising in another stagnant fluid. The ... more The test case concerns the simulation of a fluid inclusion rising in another stagnant fluid. The transient rise velocity, and the steadystate rise velocity and shape should be compared to the results obtained with an accurate numerical technique.

ABSTRACT A dynamic evaporating contact line model for perfectly wetting fluids is built. This mod... more ABSTRACT A dynamic evaporating contact line model for perfectly wetting fluids is built. This model includes the disjoining pressure, surface tension, recoil pressure, interface resistance and viscous stress. A numerical method is used to solve the set of equations, including the two-dimensional diffusion-convection heat transfer problem. We compute the macroscopic contact angle and the overall evaporation heat transfer up to a fixed macroscopic length scale and describe the governing phenomena. We found that the motion of the contact line can lead to a tremendous increase of the local heat flux.

Multiphase Science and Technology, 2004

This test case is primarily dedicated to check the ability of a numerical method to simulate cont... more This test case is primarily dedicated to check the ability of a numerical method to simulate contact line effects, in particular the contact line hysteresis. It consists in computing the conditions for which a twodimensional droplet sticks or slides on an inclined wall.

Multiphase Science and Technology, 2004

This test case describes the theoretical solutions of three simple free boundary problems: the co... more This test case describes the theoretical solutions of three simple free boundary problems: the collapse of a vapor bubble in a subcooled liquid, the initial stage of the growth of a vapor bubble in a superheated liquid, and finally, the thermally controlled growth of a vapor bubble. It is requested to compute the bubble radius as well as the interface temperature and speed of displacement.

La Houille Blanche, 2003

Physical and numerical modeling of a dynamic contact line with phase-change: A dynamic contact li... more Physical and numerical modeling of a dynamic contact line with phase-change: A dynamic contact line model is built, using a slip condition at small scale. This model includes heat transfer in the solid and the liquid, recoil pressure and interface resistance. The effect of contact line displacement and phase change on the contact angle and the heat flux is studied. Different regimes are investigated, depending on physical and geometrical parameters.

Transport in Porous Media, 1989

The macroscopic description of the dynamics of two immiscible fluids flowing through a deformable... more The macroscopic description of the dynamics of two immiscible fluids flowing through a deformable porous medium is obtained from the description of the pore scale using the homogenization theory of periodic structures. The result is a generalization of the description of saturated porous media with a BIOT structure. The homogenization process permits the complete determination of the effective parameters and the clarification of the couplings between the different phases. Two simple examples are presented for the generalized Darcy flows. Special care is taken concerning the significance of the volume averaged stress, as provided by the homogenization process. It is shown that the physical stress is different from the volume averaged stress.

International Journal of Engineering Science, 1989

International Journal for Numerical Methods in Fluids, 2008

In the framework of numerical study of multiphase flows, different front-capturing methods are co... more In the framework of numerical study of multiphase flows, different front-capturing methods are compared. Two different approaches dealing with the incompressibility constraint will be compared, too. Then, every technique is tested on several relevant test cases in order to make a comparison. The surface tension treatment is evaluated for each method and every front-capturing method is tested on a case where turbulence is well developed. Finally, every method is studied through a phase inversion which is an unsteady and turbulent test-case.

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.

Computers & Fluids, 2012

ABSTRACT Among the various direct numerical simulation (DNS) methods dedicated to multiphase flow... more ABSTRACT Among the various direct numerical simulation (DNS) methods dedicated to multiphase flow, the front-tracking methods that use a Lagrangian mesh to describe explicitly the interfaces are generally considered as a very accurate and complex method. In this family of methods, while a fine Lagrangian mesh is desirable for a better representation of the interfacial area, the surface forces and the bubble or droplet volume, one cannot arbitrarily choose the Lagrangian mesh size. Indeed, the Lagrangian mesh displacement algorithm is unstable if the number of Lagrangian degrees of freedom does not match the number of involved Eulerian velocity points. As a consequence, in traditional front-tracking implementations, an accurate description of the interfaces is expensive in terms of Eulerian mesh cells. We demonstrate that a front-tracking interface smoothing (FTIS) method can reduce the constraints on the mesh sizes. It consists in damping the highest spatial frequency components of the Lagrangian mesh to compensate for the lack of Eulerian velocity points. The test case of fundamental proper frequency of a bubble proves the validity of the FTIS method. An example of a 3D-bubble rising shows the interest and the potential applications of the FTIS method.

Chemical Engineering Science, 2012

ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover acti... more ABSTRACT Oxalic precipitation is usually applied to process radioactive wastes or to recover actinides from a multicomponent solution. Due to their later handling and use, actinide precipitates have to satisfy strict requirements. In nuclear environment where experiments are limited, simulation may be the only way to test different industrial configurations in order to adjust industrial campaigns. In this manuscript, the modelling of the tetravalent uranium oxalate precipitation in an unbaffled reactor is achieved using a hybrid multizonal/CFD model. The population balance is solved according to the moment method in a multizonal model entirely parameterised through computational fluid dynamics calculations based on large-eddy simulation (LES) and a sub-grid model of micromixing. The modelling is applied to show how the specificity of flow field in an unbaffled reactor can have a noticeable effect on the uranium oxalate properties.

Chemical Engineering Science, 2010

This article deals with the large-eddy simulation (LES) of a complex turbulent free-surface flow ... more This article deals with the large-eddy simulation (LES) of a complex turbulent free-surface flow in an unbaffled mixing tank reactor. The free-surface vortex generated in such a configuration is captured using a front-tracking method, while the stirrer is modelled with an immersed boundary condition technique. Comparisons of mean and fluctuating velocities show good agreement with both theory and experimental laser

This communication reports on the potential application of Large Eddy Simulation in the calculati... more This communication reports on the potential application of Large Eddy Simulation 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 lower 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 interface and turbulence. The complete filtered two-phase flow equations are formulated to deal with turbulence at the interface. Explicit filtering of 2D and 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.

Multiphase Science and Technology, 2004

The two-layer laminar Poiseuille flow is suggested as a case test. Two superimposed layers of vis... more The two-layer laminar Poiseuille flow is suggested as a case test. Two superimposed layers of viscous fluids separated by a flat interface are flowing in a horizontal channels. The analytical solution is provided.