Self-induced vortex ring dynamics in subsonic rectangular jets

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Abstract
The development in space and time of vortex rings in low aspect-ratio (AR) rectangular jets is investigated. By design, the present studies isolate the self-induced ring dynamics from effects of unsteady events otherwise present upstream and downstream of the rings in developed jets. The simulations show that the vortex rings undergo quite regular self-induced nonplanar deformations, approximately recovering their shape and flatness with axis rotated with respect to their initial configuration. The axis-rotation periods are in good agreement with previously reported data for pseudoelliptic rings, and exhibit nearly linear growth rate as a function of AR. For the larger aspect-ratio case studied (AR=4), bifurcation of the ring due to vortex reconnection into roughly round rings is observed, followed by collision of the split rings and a new reconnection process, suggesting pathways for transition to turbulence based on self-induced vortex deformations and reconnections.