The Many Faces of Vortices

E. Krause

Fluid flow motion is often dominated by vortices. They occur in a great variety of shapes and sizes, influencing the flow with their low pressure in the vortex core, and exerting suction forces on solid fluid boundaries of technical structures, devices, and machines. They are also present in the flows of rivers, oceanic currents, and atmospheric circulations. They are used to generate the lift of airplanes, but they also can develop extremely destructive power, as, for example, in von Kбrmбn streets, alleys of vortices shed periodically from structures in cross-winds, often strong enough to cause oscillations. While the von Kбrmбn vortices have their axes normal to the oncoming stream, longitudinal vortices orient their axes parallel to it. They are generated by the tips of helicopter blades, causing that unpleasant chopper noise, and by the wing tips of aircraft, at times delaying the starting and landing frequencies at airports. Vortices can form rings and loops such as, for example, a smoke ring, which can easily blow out a candle light from a great distance. Some of the many features of vortical flows observed are discussed in this article...

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