Analysis of the large-scale circulation and the boundary layers in turbulent Rayleigh-Benard convection

Abstract

In the present study direct numerical simulations (DNS) of turbulent Rayleigh-Benard convection in a cube with 8e6 <= Ra <= 1e9 and Pr = 4.38 are analysed. The Re-Ra-scaling of the large-scale circulation (LSC) and its local velocity distribution are investigated, revealing that the LSC velocities are non-constant along its path length, leading to slightly different Re-Ra-scalings based on a local point measurement and the mean properties of the LSC. It is shown that the simulation results are close to the theoretical prediction Re ~ Nu^2 for Prandtl-Blasius boundary layer dominated regimes. The scaling of side-wall and horizontal plate boundary layer thicknesses is investigated in order to test the theoretical prediction by Grossmann & Lohse JFM 486 (2003). It is observed that delta_{sw} / delta_p follows the prediction for 'laterally restricted' flow, since delta_{sw} / delta_p ~ const.