Numerical Analysis of Turbulent Rayleigh-bénard Convection on the Base of the Large Eddy Simulation Technique

Nowadays there are wide possibilities to perform numerical studies of turbulent natural convection flows on the base of 3D unsteady formulations [1]. Direct Numerical Simulation (DNS) is the most attractive and reliable approach for getting a detailed knowledge on convection [2, 3]. However, DNS applications are practically limited by the case of simplified geometry and/or the Rayleigh numbers not exceeding 10. Results of unsteady computations based on the Reynolds-Averaged Navier-Stokes (RANS) equations are very sensitive to the turbulence model choice. Expectations for covering the range of high Rayleigh numbers are traditionally concerned with Large Eddy Simulation (LES). However, in case of LES applications to wall-bounded flows the major difficulties are associated with the treatment of the near-wall layers [4, 5]. Typically approximate wall boundary conditions (wall functions) are used to keep reasonable computational grids. But wall functions introduce further empiricism in calculations and may lead to uncertain results. In order to overcome these drawbacks recent works proposed hybrid techniques combining RANS and LES approaches [5]. The present work is aimed at numerical simulation of strongly turbulent Rayleigh-Bénard (RB) convection in confined enclosures of aspect ratio 1. Mercury and water, characterized by essentially different Prandtl numbers, have been chosen as test fluids. Turbulence modelling is performed with a RANS/LES hybridization involving the equation of the kinetic energy of unresolved motion. Results of computations are presented in comparison with experimental data.