vortex ring
noun
a stable perturbation in a fluid that takes the form of a torus in which the flow rotates in the section of the torus so that the pressure difference between the inside and outside of the torus balances body forces. The best-known vortex ring is a smoke ring
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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Examples from the Web for vortex ring
Historical Examples of vortex ring
Through a vortex-ring or tube, the fluid circulates in closed lines of flow, each one of which is laced through the tube.
Lord KelvinAndrew Gray
A vortex-ring produced in the air behaves in the most surprising manner.
The Machinery of the UniverseAmos Emerson Dolbear
Such a vortex-ring is made by the smoker who purses his lips into a round hole and sends out a puff of smoke.
The Unseen World and Other EssaysJohn Fiske
Now this is just what a vortex-ring would do in an incompressible frictionless fluid.
The Unseen World and Other EssaysJohn Fiske
It is certainly possible roughly to conceive how such a structure as a vortex-ring in the ether might be formed.
The Machinery of the UniverseAmos Emerson Dolbear