Three-Dimensional Visualization of the Interaction between a Vortex Ring and a Stratified Interface: The Evolution of the Density Field

The study of vortex-ring-induced stratified mixing has long played a key role in understanding externally-forced, stratified turbulent mixing. While several studies have investigated the dynamical evolution of a such a stratified system, this paper presents an experimental investigation of the three-dimensional mechanical evolution of these vortex rings with the specific goal of a understanding how vortex rings induce mixing of the density field. Through the use of modern imaging techniques, we reconstruct a full, three-dimensional, time-resolved velocity field encapsulating the interaction of a vortex ring with a stratified interface. Using a numerical scheme, we back out the density field from the experimentally determined velocity field. This work agrees with many of the previous twodimensional studies, while capturing the three-dimensional instabilities of the system. The horizontally-averaged vertical buoyancy flux is then presented as a function of time which helps to explain the interface sharpening observed elsewhere.