The trapping and escape of buoyant vortex rings in sharply stratified   fluids
  In this fluid dynamics video we study the dynamics of miscible vortex rings falling in ambient strongly (near two-layer) stratified fluid. Experiments and direct numerical simulations using the variable density Navier-Stokes (VARDEN) solver are presented and compared. Critical phenomena are identified depending upon the key parameters of the experiment (fluid and ring densities, upper layer vortex travel distance, etc) in which the descending dense vortex ring may experience complete trapping, partial trapping, or fissioning into a cascade of smaller vortices. The interaction of the vortex ring with the upper layer fluids leads to viscous entrainment which alters the effective buoyancy of the ring. Upon impinging on a density transition, the entrained fluid imparts different dynamics as it attempts to regain equilibrium leading to the critical behaviors. 
R. Camassa, S. Khatri, R. McLaughlin, K. Mertens, E. Monbureau, D.   Nenon, C. Smith, C. Viotti, B.White
physics.flu-dyn