Direct numerical simulations of the transition between rotation- to buoyancy-dominated regimes in rotating Rayleigh–Bénard convection

The flow transition between rotation-dominated and buoyancy-dominated regimes in rotating Rayleigh–Bénard convection is investigated via direct numerical simulations (DNS), for laterally periodic domains and no-slip top and bottom boundary conditions. The comprehensive transition pathway is realized by increasing the thermal driving force (Rayleigh number, Ra) over five orders of magnitude, for Ra=5×106 to 5×1011, and Ekman number Ek from 1.5×10−6 to 5×10−5, and Prandtl number Pr=1. During the transition, the typical flow states, i.e., cells, Taylor columns, plumes, rotation-affected turbulence, and buoyancy-dominated turbulence are revealed. The thermal and viscous boundary layer (BL) statistics, interior temperature gradient, and scaling relations for the heat and momentum transports (reflected in the Nusselt number Nu and Reynolds number Re) as well as the convective length scale are investigated across various flow regimes. It is demonstrated that the thermal BL thickness decreases monotonically and becomes thinner than the viscous BL thickness in the buoyancy-dominated regime. Moreover, the heat and momentum transport scaling relations during the transition are shown to agree well with the recently proposed unifying transition scaling model, which is based on the balance of the thermal and viscous (Ekman) BL thicknesses (R. Ecke & O. Shishkina, Annu. Rev. Fluid Mech. 55 (2023)).