Effects of weak centrifugal force in turbulent rotating thermal convection

This experimental study aims to clarify how and when a weak centrifugal force affects the turbulent rotating thermal convection system. For the bulk flow, the weak centrifugal effect is significant on long-time averaged flow fields, contrasting sharply with its negligible effect on the instantaneous fields. As for the sidewall flow, it is found that properties of the boundary zonal flow are influenced by the weak centrifugal force appreciably. The onset Froude number $\textit{Fr}_c^{\textit{local}}$ , signalling when the weak centrifugal effects start to set in, is found to scale with Rayleigh number $Ra$ as $\textit{Fr}_c^{\textit{local}}\sim Ra^{0.55}$ over approximately two and a half decades of $Ra$ . The underlying mechanism for this robust scaling is captured by the mechanism of local force balance, which involves three unknown local scales. With the help of both a viscous–Archimedean–Coriolis argument and the experimental data, these local scales are successfully resolved to reveal a consistent result with this 0.55 scaling.