TURBULENCE-BASED EXPRESSION FOR THE ENTRAINMENT COEFFICIENT FOR TWO-LAYERED STRATIFIED FLOWS.

An investigation has been undertaken of stably stratified two-layer flows where one layer with fully developed turbulence entrains non-turbulent fluid of the second layer. The velocity of entrainment has been measured for four types of two-layered flows and analyzed on the basis of the view that the turbulence plays an essential role in the entrainment process. These flows involve turbulence generated by an oscillating-grid, by shear flow of an upper-layer and by wind-induced flows with and without surface waves. The turbulence intensity and integral lengthscale have been chosen as characteristic quantities of the turbulence, and the density difference between the two fluids provides an effective buoyancy.