The goal of this paper is to report the effect of shear, and the direction of shear, on rates of vertical buoyancy flux in stably stratified grid-generated turbulence. Results from an experimental study of turbulent, density stratified, sheared flow are presented. The flow field is a combination of decaying grid-generated turbulence, stable density stratification, and shear production of turbulence. Turbulent mixing is at the heart of many industrial processes. For example, rapid mixing is essential in the chemical engineering industry to optimize yields from reacting chemicals. Density stratification is common in the ocean and atmosphere. Variations in temperature and salinity in the ocean, and temperature and humidity in the atmosphere, result in density gradients. Stable stratification influences the dynamics as a kinetic energy sink because energy is sapped by work against gravity. Thus, turbulent mixing rates in a density-stratified fluid can be severely attenuated relative to the case without density stratification. Velocity shear, common in the environment, is a source of energy, and therefore turbulent mixing rates are greater when shear is present. However, turbulent mixing rates depend on the relative strengths of shear and density stratification, and on initial conditions as expressed by the ratio of turbulent potential to vertical kinetic energies.
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