Mixing dynamics of a sharp density interface in mean shear free homogeneous isotropic turbulence

The interaction of a sharp density interface with homogeneous isotropic turbulence with negligible mean shear is a fundamental problem with broad environmental, geophysical, and industrial relevance. Despite extensive research in this field, critical aspects of this problem have yet to be uncovered. We present laboratory experiments of a two-layer system conducted in a water tank in which a random jet array generates homogeneous isotropic turbulence with negligible mean flow. The turbulent layer, composed of an alcohol-water mixture, overlies a quiescent dense layer of a sugar-water mixture. Experiments are performed under varying density differences and turbulence levels to comprehensively characterize the dynamics. Simultaneous measurements of velocity and density fields, using particle image velocimetry (PIV) and laser-induced fluorescence (LIF), respectively, allow us to track the evolution of the turbulent flow and interface over time. We then quantify mixing efficiencies and their dependence on non-dimensional parameters such as the Richardson and buoyancy Reynolds numbers. Further, we identify distinct mixing scenarios and their relationship to these governing parameters. These findings contribute to a deeper understanding of density interface dynamics in turbulent environments.