Mixing efficiency in stably stratified growing turbulence

Abstract

Nearly steady state mixing efficiencies, as characterized by the flux Richardson number R f , have been measured in stably stratified, turbulent, uniform gradient shear flows. The turbulent dissipation rate ϵ, the vertical mass and momentum fluxes and , and the mean and rms density and velocity fluctuations were obtained from simultaneous single point measurements of velocity and density. R f and the gradient Richardson number Ri were calculated at a number of positions in the spatially evolving shear flow. Within the investigated range of stabilities 0.02< Ri <0.08, R f was observed to increase with Ri . It is found that the length scale arguments successfully applied by Rohr et al . (1984) to the case of decaying, stably stratified, unsheared grid turbulence can also account for the overall behavior of the mixing efficiency ( R f ) as a function of stability ( Ri ) in the present case of growing, stably stratified, uniform mean shear turbulence.