Direct Simulation of Double-Diffusive Layered Convection

A two-layer, salt-stratified system destabilized and mixed by lateral heating and cooling is simulated numerically using a spectral methodology. As noted in previous studies, the mixing time is delayed as the stabilizing buoyancy ratio increases, and as the Rayleigh number decreases. 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 layer. 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 method are in relatively good agreement with experimental data.