2-DIMENSIONAL TURBULENCE IN HOMOGENEOUS AND STRATIFIED SHEAR LAYERS

We investigate the development of two-dimensional turbulence in a temp orally-growing shear layer. This is accomplished through the applicati on of numerical simulation techniques in computational domains which a ccommodate many wavelengths of the primary Kelvin-Helmholtz instabilit y. Both homogeneous and density-stratified flows are considered. Sprea ding rates of homogeneous and stratified shear layers are computed and compared with the results of laboratory experiments. We show that she ar-driven vortex mergers generate downscale enstrophy cascades through filamentation, as do the mergers which occur in the isotropic case. I n the long-time limit, homogeneous shear layers are dominated by a sin gle coherent vortex. The addition of even a slight degree of stratific ation alters the vortex dynamics dramatically. Vortex filaments which are generated and stabilized by the straining deformations between adj acent large vortices are reinforced by the baroclinic torque. As a res ult, these structures ultimately dominate the vorticity field in weakl y-stratified flows. In strongly-stratified cases, pairing instability is suppressed and the flow relaxes quickly to a stable parallel state.