Spatial variations of the mean and statistical quantities in the thermal boundary layers of turbulent convection

Abstract:

An experimental study of Rayleigh-Bénard turbulent convection in a cubic cell is presented. We measure the mean temperature profiles, the root mean square (RMS) temperature profiles and the thermal boundary layer thickness for various values of the Rayleigh number Ra and at various positions x along the direction of large-scale circulation (LSC), using water as the working fluid. The scaled mean temperature profiles measured at the same Ra but different x are found to be self-similar, but those measured at different Ra do not show a universal form. In contrast, RMS temperature profiles measured at the same position but different Ra appear to show an invariant form, whereas those with different x but of the same Ra could not be scaled onto a single curve. Irrespective of the measuring positions and Ra, the RMS profiles show a peak value around the boundary layer thickness, and their gradients at bottom surface increase monotonically in the direction of LSC and with increasing Ra.