Thermal boundary layer dynamics in low-Prandtl-number Rayleigh-Benard convection

In this experimental study, we explore the dynamics of the thermal boundary layer in liquid metal Rayleigh-Benard convection, covering the parameter ranges of 0.026 <= Prandtl numbers (Pr) <= 0.033 and Rayleigh numbers (Ra) up to 2.9 x 10(9). Our research focuses on characterising the thermal boundary layer near the top plate of a cylindrical convection cell with an aspect ratio of 0.5, distinguishing between two distinct regions: the shear-dominated region around the centre of the top plate and a location near the side wall where the boundary layer is expected to be affected by the impact or ejection of thermal plumes. The dependencies of the boundary layer thickness on Ra at these positions reveal deviating scaling exponents with the difference diminishing as Ra increases. We find stronger fluctuations in the boundary layer and increasing deviation from the Prandtl-Blasius-Pohlhausen profile with increasing Ra, as well as in the measurements outside the centre region. Our data illustrate the complex interplay between flow dynamics and thermal transport in low-Pr convection.