Vortex Rings
Vortex rings are fluid structures with concentrated vorticity, having toroidal a shape,
with material particles rotating about a common axis.
In the case of vortex rings, this common axis of rotation forms a closed loop,
i.e, a toroidal fluid structure with a poloidal flow pattern.
They are a class of stable fluid structures that appear in different fluid flows and are ubiquitous in high Reynolds number flows, and they appear abundantly in nature, biological and engineering flows.