Large Scale Vortices in the Rotating Rayleigh-Benard setup with no-slip boundaries*

In rotating Rayleigh-B\'enard (RRB) convection, the buoyancy-driven flow between two horizontal plates subject to rotation, different regimes are accessible depending on the strength of buoyancy and rotation. Under intense forcing (high Rayleigh number $Ra$), turbulent convection is obtained and, if rotation is strong enough (low Ekman number $Ek$), vertical motions are greatly suppressed. This allows for a quasi-two-dimensional turbulent state. In such conditions an inverse energy cascade is possible, leading to large-scale vortices (LSVs) in the flow. LSVs have been observed for stress-free top/bottom boundaries, but not yet for the no-slip case until now. In the latter, Ekman pumping from the viscous layer induces vertical velocities that affect the 2D flow. This vertical component however is attenuated when rotation is increased. We directly simulate RRB flow at $Ek\sim10^{-7}$ and $Ra\sim10^{10}-10^{12}$ in a horizontally periodic box with no-slip boundaries for two fluids with Prandtl number $Pr=0.1$ (towards liquid metals) and 5.2 (water). We show that LSVs are possible when viscous effects are strongly confined to the boundaries and no longer influence the bulk flow. At both $Pr$s, the flow is quasi-2D and a domain-filling vortex dipole is observed.