Interfacial Dynamics in Mean Shear Free Turbulence

The presence of turbulence near a density interface is ubiquitous in oceanic and atmospheric environments, and plays a crucial role in the dynamics of these environments. Turbulence enhances irreversible mixing across density interfaces by increasing the interfacial area through the induction of various instabilities and internal wave generation. Regions of low mean shear turbulence adjacent to a stably stratified sharp density interface have been identified in bay areas (Hodges et al. 2011). Despite its significance, there are still many unknowns about this fundamental flow. In this study, we perform a series of laboratory experiments to investigate the driving mechanisms in the evolution of a density interface due to turbulence present in the ambient. To do so, we generate nearly homogeneous isotropic turbulence with negligible mean shear using a random jet array (RJA) in a two-layered flow. The top layer, continuously stirred by the RJA, is located above the dense quiescent layer. We use particle image velocimetry (PIV) to measure the velocity of the flow and turbulence statistics such as turbulent kinetic energy, integral length scale and dissipation rate. Simultaneously, we incorporate laser induced fluorescence to find the location of the interface as it evolves through time. By modifying the flow characteristics, such as turbulent Reynolds number, and the density stratification, which affects the buoyancy Reynolds number and Richardson number, we are able to identify interfacial dynamics and quantify mixing rate and efficiency in different scenarios.