Flow regime transitions in rotating Rayleigh–Bénard convection induced by Navier slip boundaries

We investigate the role of slippery boundaries, quantified by the Navier boundary friction coefficient $\beta$ , in regulating heat transport and flow structures in rotating Rayleigh–Bénard convection. Owing to the Ekman pumping effect arising from viscous boundary layers that is intensified with increasing boundary friction, it is found that the properties of global heat transport exhibit two distinct parameter regimes separated by a transitional Rayleigh number ( $ \textit{Ra}_t$ ). In the rotation-dominated regime ( $ \textit{Ra} \lt \textit{Ra}_t$ ), enhanced viscous friction increases the efficiency of Ekman pumping, significantly elevating the Nusselt number and lowering the convection onset threshold. Conversely, in the buoyancy-dominated regime ( $ \textit{Ra} \gt \textit{Ra}_t$ ), boundary-induced viscous dissipation suppresses convective motions, thereby reducing heat transport. Large-scale vortices (LSVs), prevalent under free-slip conditions, progressively dissipate as $\beta$ increases, revealing that viscous friction disrupts the inverse energy cascade from baroclinic to barotropic modes. Through kinetic energy partitioning analysis, the transition between quasi-two-dimensional and three-dimensional turbulent states is identified, with the parameter $\beta _{\textit{cr}}$ following a generic scaling relation on the Prandtl (Pr) and Ekman (Ek) numbers $\beta _{\textit{cr}}\sim \textit{Pr}^{-0.67}\textit{Ek}^{-1.18}$ . This relation enables us to predict LSV emergence across different parameter spaces. Furthermore, it is reported that the heat-transport scaling exponent, the convection onset and the partitioning of kinetic energy between barotropic and baroclinic components undergo a smooth flow transition at $\beta _{\textit{cr}}$ . These results also indicate a direct correlation between Ekman pumping efficacy and the friction coefficient $\beta$ , demonstrating that controlling boundary friction can modulate global transport properties and reshape flow structures.