Boundary layers in rotating weakly turbulent Rayleigh–Bénard convection

The effect of rotation on the boundary layers (BLs) in a Rayleigh–Bénard system at a relatively low Rayleigh number, i.e., Ra=4×107, is studied for different Pr by direct numerical simulations and the results are compared with laminar BL theory. In this regime, we find a smooth onset of the heat transfer enhancement as function of increasing rotation rate. We study this regime in detail and introduce a model based on the Grossmann–Lohse theory to describe the heat transfer enhancement as function of the rotation rate for this relatively low Ra number regime and weak background rotation Ro≳1. The smooth onset of heat transfer enhancement observed here is in contrast to the sharp onset observed at larger Ra≳108 by Stevens et al. [Phys. Rev. Lett. 103, 024503 (2009)], although only a small shift in the Ra-Ro-Pr phase space is involved.