DIRECT SIMULATION OF DOUBLE-DIFFUSIVE LAYERED CONVECTION

A two-layer, salt-stratified system destabilized and mired by lateral heating and cooling is simulated numerically using a spectral methodol ogy. As noted in previous studies, the mixing time is delayed as the s tabilizing buoyancy ratio increases, and as the Rayleigh number decrea ses. Depending on the regime of operation, however, distinct physical mechanisms are responsible for interface erosion and system mixing. At low Ra, erosion is gradual with overlying (underlying) fluid sheared from the interface and mixed into the adjacent thermally convecting la yer. At high Ra, an intermittent mechanism is predicted to occur with solutally distinct plumes bombarding the interface and ejecting fluid into the convecting layers. Predictions obtained with the spectral met hod are in relatively good agreement with experimental data.