Vortex ring
TORUS-SHAPED VORTEX IN A FLUID OR GAS
Spherical vortex; Hill's vortex; Vortex ringstate; Toroidal vortex; Hill's Spherical Vortex
A vortex ring, also called a toroidal vortex, is a torus-shaped vortex in a fluid; that is, a region where the fluid mostly spins around an imaginary axis line that forms a closed loop. The dominant flow in a vortex ring is said to be toroidal, more precisely poloidal.