Evolution of Turbulent Vortex Rings in Uniformly Stratified Environments*

Vortex-induced stratified mixing is a topic that has received significant attention.  Past studies have examined vortex rings impacting a density interface, traveling at an oblique angle through a stratified region, and laminar rings traveling through either a sharp pycnocline or a continuously stratified region.  In this study laboratory experiments were performed to investigate the long-time behavior of turbulent vortex rings in both constant density and uniformly stratified environments.  Existing empirical models of ring behavior in constant density environments were compared to the extant data and were extended to turbulent rings traveling through a uniformly stratified region.  The vortex rings were found to exhibit three distinct behaviors, primarily dependent upon the local Froude number of the ring as it entered the stratified region: (1) expansion and collapse while transitioning into the uniformly stratified region, (2) rapid decrease in velocity and core radius and stopping within the uniformly stratified region, or (3) traveling totally through the stratified layer.  In addition, the degree of transfer of energy from the vortex ring to the internal wavefield was quantified.