Rapidly rotating turbulent Rayleigh-Bénard convection

Abstract

Turbulent Boussinesq convection under the influence of rapid rotation (i.e. with comparable characteristic rotation and convection timescales) is studied. The transition to turbulence proceeds through a relatively simple bifurcation sequence, starting with unstable convection rolls at moderate Rayleigh (Ra) and Taylor numbers (Ta) and culminating in a state dominated by coherent plume structures at highRaandTa. Like non-rotating turbulent convection, the rapidly rotating state exhibits a simple power-law dependence onRafor all statistical properties of the flow. When the fluid layer is bounded by no-slip surfaces, the convective heat transport (Nu− 1, whereNuis the Nusselt number) exhibits scaling withRa2/7similar to non-rotating laboratory experiments. When the boundaries are stress free, the heat transport obeys ‘classical’ scaling (Ra1/3) for a limited range inRa, then appears to undergo a transition to a different law atRa≈ 4 × 107. Important dynamical differences between rotating and non-rotating convection are observed: aside from the (expected) differences in the boundary layers due to Ekman pumping effects, angular momentum conservation forces all plume structures created at flow-convergent sites of the heated and cooled boundaries to spin-up cyclonically; the resulting plume/cyclones undergo strong vortex-vortex interactions which dramatically alter the mean state of the flow and result in a finite background temperature gradient asRa→ ∞, holdingRa/Tafixed.