A Kármán vortex street is a series of whirlwinds produced by a cylindrical object, such as a tower, in the wind. The stream of miniature tornadoes travels downwind of the obstacle at regular intervals, which is why the effect is known as a street. These little-known streets can destroy buildings.
The effect was discovered in the early 1900s by the Hungarian physicist Theodore von Kármán, who was investigating why bridge supports and buildings spontaneously vibrate in high winds. Kármán found that air flowing around an obstacle broke away into distinct whirlwinds. At a particular wind speed, the forces involved produce resonance, causing wires to sing in the wind, or towers to wobble.
A powerful Kármán vortex street occurred at Ferrybridge power station in West Yorkshire, on 1 November 1965. Eight cooling towers, each over a hundred metres tall, had been built only three years previously, but 80mph gusts had a catastrophic effect. The four towers on the windward side stood firm, but those behind were buffeted by vortices from those upwind. At 10.30am one tower collapsed, followed by two others over the next hour. Fire damaged the remaining five towers. Fortunately, nobody was hurt.
When the matter was raised in the House of Lords, it was suggested that a Labour wind had brought down Tory-built towers. A later investigation found that the wind safety calculations were based on a single isolated tower, and neglected the possible effects of a Kármán vortex street on a group of them.
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