Buoyant turbulent mixing in shear layers

Abstract

Buoyancy effects in unstably stratified mixing layers express themselves through gravity currents of heavy fluid which propagate in an ambient lighter fluid. These currents are encountered in numerous geophysical flows, industrial safety and environmental protection issues. During transition to turbulence a strong distortion of the separating interface between regions containing `heavy' or `light' fluid arises. The complexity of this interface will be used to monitor the progress of the mixing. We concentrate on the enhancement of surface-area and `surface-wrinkling' of the separating interface as a result of gravity-effects. We also show that this process can be simulated quite accurately using large-eddy simulation with dynamic subgrid modeling. However, the subgrid resolution, defined as the ratio between filter-width Delta and grid-spacing h, should be sufficiently high to avoid contamination due to spatial discretization error effects.