Matched boundary layers in turbulent Rayleigh-Bénard convection of mercury

Abstract

We analyzed temperature time series recorded in different positions across the boundary layers of a Rayleigh-B\'enard convection cell using mercury (Pr=0.024) for Rayleigh numbers (Ra) ranging from ${10}^{6}$ to ${10}^{8}$. In the whole range of Ra, several nondimensional quantities have unique, Ra-invariant profiles, if distance is normalized by the thermal boundary layer thickness. This indicates an asymptotic regime of thermal turbulence in which two boundary layers are coupled. Skewness and its time derivative of thermal fluctuations reveal that temperature fluctuations are not buoyancy driven but passively swept by the mean circulation in most of the cell.