Studies on the mixing in a density-stratified shear flow

The mixing in a two-layered density-stratified shear flow in a flume 40-meters long, with a cross-section of 110 cm wide by 60 cm deep was measured. The relative density difference between the layers was 0.001 or less. The initial mixing layer which developed at the inlet was found to be dominated by large, two-dimensional vortex structures. Much less turbulent mixing took place in the stratified flows than homogeneous flows. The turbulence was dominated by large turbulent bursts, during which the vertical turbulent transport of momentum, heat and turbulent kinetic energy are many times larger than their mean values. These bursts were responsible for most of the total turbulent transport of momentum, heat and turbulent kinetic energy, even though the bursts were found only intermittently. In almost all cases, the rate at which the potential energy of the fluid increased due to turbulent mixing was much less than the estimated rate of viscous dissipation of turbulent kinetic energy.