Phenomena

Forming a Vortex

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Vortex rings show up remarkably often in nature. In addition to being the playthings of dolphins, whales, scuba divers, humans, and swimmers, vortex rings appear in volcanic outbursts and spore-spreading peat mosses. Vortex rings even occur in blood flow through the human left ventricle in the heart. In each of these cases, the vortex ring is formed by impulsively accelerating fluid through a narrow opening, like the dolphin’s blowhole. The fluid at the edge of injected jet is slowed by friction with the quiescent surrounding fluid. The fluid at the edge of the jet then slips around the sides and into the wake of the faster-moving fluid, where it’s accelerated through the middle of the forming vortex ring. This spinning from the inside-out and back-in persists as long as the vortex is intact, and is part of what keeps the ring from dissipating. (Video credit: SeaWorld; submitted by John C.)

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