This paper conducts a Large Eddy Simulation (LES) of Rayleigh Bénard convection in a cubic cavity based on the WMLES S-Omega subgrid-scale model. For a cubic cavity with a vertical temperature difference of 6.7&#...This paper conducts a Large Eddy Simulation (LES) of Rayleigh Bénard convection in a cubic cavity based on the WMLES S-Omega subgrid-scale model. For a cubic cavity with a vertical temperature difference of 6.7°C and 20°C, the velocity pulsation profiles and the mean velocity profiles of the vertical section in the middle of the cubic cavity were simulated, respectively. And they are consistent with the experiment results. Furthermore, the mean velocity field of the vertical cross-section in the middle of the cavity was calculated. Structures of the mean velocity field in the two cases are similar. A counterclockwise large vortex is found to occupy the cavity, and there are two small clockwise vortices in the lower left and upper right corners, and the mean velocity fields at two different temperature differences are consistent with the experimental results. The two-dimensional instantaneous temperature field and mean temperature field with different cross-sections in the z-direction, as well as the three-dimensional instantaneous isothermal surface structure, indicate that the large-scale circulation motion within the cubic cavity is moving diagonally. In addition, the structure of the mean streamline also illustrates this viewpoint. For the reverse vortex formed at two corners in the mean streamline structure, we used the Q criterion to identify and obtain two vortex structures similar to boomerangs. The basic turbulent structure in RB thermal convection includes the rising and falling plumes generated by buoyancy effects.展开更多
We report the results of the direct numerical simulations of two-dimensional Rayleigh-Bénard convection(RBC)in order to study the influence of the periodic(PD)and confined(CF)samples on the heat transport Nu.The ...We report the results of the direct numerical simulations of two-dimensional Rayleigh-Bénard convection(RBC)in order to study the influence of the periodic(PD)and confined(CF)samples on the heat transport Nu.The numerical study is conducted with the Rayleigh number(Ra)varied in the range 10^(6)≤Ra≤10^(9) at a fixed Prandtl number Pr=4.3 and aspect ratio Γ=2 with the no-slip(NS)and freeslip(FS)plates.There exists a zonal flow for Ra≥3×10^(6) with the free-slip plates in the periodic sample.In all the other cases,the flow is the closed large-scale circulation(closed LSC).The striking features are that the heat transport Nu is influenced and the temperature profiles do not be influenced when the flow pattern is zonal flow.展开更多
In this paper,we develop and test a unified hybrid LES/URANS turbulence model with two different Large Eddy Simulation(LES)turbulence models.The numerical algorithm is based on the Boundary Element Method.In the exist...In this paper,we develop and test a unified hybrid LES/URANS turbulence model with two different Large Eddy Simulation(LES)turbulence models.The numerical algorithm is based on the Boundary Element Method.In the existing hybrid LES/URANS turbulence model we implemented a new Smagorinsky LES turbulence model.The hybrid LES/URANS turbulence model is unified,which means that the LES/URANS interface is changed dynamically during simulation using a physical quantity.In order to define the interface between LES and unsteady Reynolds Averaged Navier Stokes(URANS)zones during the simulation,we use the Reynolds number based on turbulent kinetic energy as a switching criterion.This means that the flow characteristics define where the sub-grid scale or URANS effective viscosity and thermal conductivity are used in the governing equations in the next time step.In unified hybrid turbulence models,only one set of governing equations is used for LES and URANS regions.The developed hybrid LES/URANS model was tested on non-isothermal,unsteady and turbulent Rayleigh-Bénard Convection and compared with an existing model,where LES is based on turbulent kinetic energy.The hybrid turbulence model was implemented within a numerical algorithm based on the Boundary-Domain Integral Method,where a single domain and sub-domain approaches were used.The numerical algorithm uses governing equations written in a velocity-vorticity form.The false transient time scheme is used for the kinematics equation.展开更多
In this paper the influence of an impressed Coriolis force field on the configuration of a turbulent Rayleigh-Bénard convection problem is investigated in an experimental and numerical study. The main purpose of ...In this paper the influence of an impressed Coriolis force field on the configuration of a turbulent Rayleigh-Bénard convection problem is investigated in an experimental and numerical study. The main purpose of both studies lie on the analysis of a possible stabilising effect of a Coriolis acceleration on the turbulent unsteady structures inside the fluid. The relative Coriolis acceleration which is caused in the atmosphere by the earth rotation is realised in the experimental study by a uniform-rotational movement of the setup in a large-scale centrifuge under hyper-gravity. The same conditions as in the atmosphere in the beginning of a twister or hurricane should be realised in the experiment. The investigated Rayleigh numbers lie between 2.33 × 106 ≤ Ra ≤ 4.32 × 107.展开更多
文摘This paper conducts a Large Eddy Simulation (LES) of Rayleigh Bénard convection in a cubic cavity based on the WMLES S-Omega subgrid-scale model. For a cubic cavity with a vertical temperature difference of 6.7°C and 20°C, the velocity pulsation profiles and the mean velocity profiles of the vertical section in the middle of the cubic cavity were simulated, respectively. And they are consistent with the experiment results. Furthermore, the mean velocity field of the vertical cross-section in the middle of the cavity was calculated. Structures of the mean velocity field in the two cases are similar. A counterclockwise large vortex is found to occupy the cavity, and there are two small clockwise vortices in the lower left and upper right corners, and the mean velocity fields at two different temperature differences are consistent with the experimental results. The two-dimensional instantaneous temperature field and mean temperature field with different cross-sections in the z-direction, as well as the three-dimensional instantaneous isothermal surface structure, indicate that the large-scale circulation motion within the cubic cavity is moving diagonally. In addition, the structure of the mean streamline also illustrates this viewpoint. For the reverse vortex formed at two corners in the mean streamline structure, we used the Q criterion to identify and obtain two vortex structures similar to boomerangs. The basic turbulent structure in RB thermal convection includes the rising and falling plumes generated by buoyancy effects.
基金supported by the Natural Science Foundation of Guangdong Province(Grant No.2020A1515011094)the Science,Technology and Innovation Commission of Shenzhen Municipality(Grant No.KQJSCX20180328165817522).
文摘We report the results of the direct numerical simulations of two-dimensional Rayleigh-Bénard convection(RBC)in order to study the influence of the periodic(PD)and confined(CF)samples on the heat transport Nu.The numerical study is conducted with the Rayleigh number(Ra)varied in the range 10^(6)≤Ra≤10^(9) at a fixed Prandtl number Pr=4.3 and aspect ratio Γ=2 with the no-slip(NS)and freeslip(FS)plates.There exists a zonal flow for Ra≥3×10^(6) with the free-slip plates in the periodic sample.In all the other cases,the flow is the closed large-scale circulation(closed LSC).The striking features are that the heat transport Nu is influenced and the temperature profiles do not be influenced when the flow pattern is zonal flow.
基金support from the Slovenian Research Agency(research core funding No.P2-0196).
文摘In this paper,we develop and test a unified hybrid LES/URANS turbulence model with two different Large Eddy Simulation(LES)turbulence models.The numerical algorithm is based on the Boundary Element Method.In the existing hybrid LES/URANS turbulence model we implemented a new Smagorinsky LES turbulence model.The hybrid LES/URANS turbulence model is unified,which means that the LES/URANS interface is changed dynamically during simulation using a physical quantity.In order to define the interface between LES and unsteady Reynolds Averaged Navier Stokes(URANS)zones during the simulation,we use the Reynolds number based on turbulent kinetic energy as a switching criterion.This means that the flow characteristics define where the sub-grid scale or URANS effective viscosity and thermal conductivity are used in the governing equations in the next time step.In unified hybrid turbulence models,only one set of governing equations is used for LES and URANS regions.The developed hybrid LES/URANS model was tested on non-isothermal,unsteady and turbulent Rayleigh-Bénard Convection and compared with an existing model,where LES is based on turbulent kinetic energy.The hybrid turbulence model was implemented within a numerical algorithm based on the Boundary-Domain Integral Method,where a single domain and sub-domain approaches were used.The numerical algorithm uses governing equations written in a velocity-vorticity form.The false transient time scheme is used for the kinematics equation.
文摘In this paper the influence of an impressed Coriolis force field on the configuration of a turbulent Rayleigh-Bénard convection problem is investigated in an experimental and numerical study. The main purpose of both studies lie on the analysis of a possible stabilising effect of a Coriolis acceleration on the turbulent unsteady structures inside the fluid. The relative Coriolis acceleration which is caused in the atmosphere by the earth rotation is realised in the experimental study by a uniform-rotational movement of the setup in a large-scale centrifuge under hyper-gravity. The same conditions as in the atmosphere in the beginning of a twister or hurricane should be realised in the experiment. The investigated Rayleigh numbers lie between 2.33 × 106 ≤ Ra ≤ 4.32 × 107.
