Influence of the lateral walls on the thermal plumes in turbulent Rayleigh-Bénard convection in rectangular containers

DNS of Rayleigh-Bénard convection have been performed in a cube for Ra up to 2.31 x 108 and compared to simulations conducted in a rectangular periodic cell. Comparison of the mean heat transfer shows only small differences after the onset of turbulence, which appear to vanish for Ra→∞. Evaluation of the contributions of the regions associated with the bulk (I), plumes and mixing layers (II) and the conductive sublayer (III) reveal that the respective contributions ar similar for Ra≥3.5x106, whereas at the lowest Ra region II dissipation rates contribute significantly more to the mean heat transfer in the cube. Significant differences are also observed in the temporal behaviour of the least-squares fit coefficient B2 of the conductive sublayer for Ra up to 3.5x106. This is also reflected by a mean temperature profile that in the cube resembles a laminar profile, whereas a turbulent one is found in the periodic cell