Vortex Formation in a Friction Layer: A Numerical Simulation

Abstract

Axially symmetric thermal convection in a rotating environment with a friction layer is investigated by numerically integrating an appropriate system of equations. The study examines the influence of the friction layer upon dry adiabatic thermal convection and the resulting vortex formation process by making comparative computer runs, with and without addition of the friction layer, for four values of ambient-vertical vorticity. The analysis shows that the addition of a friction layer has a significant influence on the resulting velocity distributions. Friction-induced radial convergence adds to the central updraft of the rising thermal and increases its rate of rise. This friction layer enhancement increases with larger rotation rates and consequently overcomes the correspondingly increased rotational suppression. The vortex height is observed to be greater for the friction layer runs. Additionally, the vortex is observed to have a smoother but less intense profile of tangential velocity with the friction layer present and breaks contact with the ground as a result of the non-slip surface boundary condition. The friction layer reduces considerably the tangential velocity of the vortex formed by the buoyant cloud under all circumstances, but the rate of rise of the cloud is hardly affected unless the environmental vorticity is in excess of 10?3 sec?1.