Jessica Paquette

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The Beautiful, Deadly Vortex That Tears Huge Buildings Apart

The Karman Vortex Street isn’t someplace you’d want to take up residence — it’s literally the path of destruction, where buildings collapse and destruction reigns. Unfortunately, under the right conditions, a Karman Vortex can follow you.

Find out how this beautiful phenomenon can take down anything in its path.

Theodore von Karman, a Hungarian physicist, spent much of the first decade of the 1900s trying to figure out why certain things — airplane wings, bridge supports, buildings, and submarines — would suddenly and spontaneously begin to vibrate. The vibration, once started, would often amp up and up until the entire structure would spin out of control or fall apart. This, understandably, was a major problem.

Karman’s first insight was that the closer to cylindrical the object’s shape was, the more it tended to vibrate. His second insight led him to turn away from the actual object and toward its medium. And after looking at the medium that moved over these objects, he noticed something.

Aerodynamics are at their best when the air (or any gas, or liquid) flows neatly around the object, conforming exactly to the object’s shape. This is why wings open with a curve and taper off behind, parting the air quickly but letting it flow over the curves and break away from the wing going pretty much directly back. By sending air streaming directly back, the object gets a push directly forward. Of course wings divert the air slightly down, giving the plane a slight lift, as well, but they still give the air an orderly path to follow.

Things get tricky, though, when a flowing medium encounters a cylinder instead of a wing. When that happens, the flow can ‘break away’ from the object at its widest point. Instead of flowing back from the object, it is directed off to one side. This break in the medium curls the other side in, before it, too, breaks away in its own dash to one side. Now, instead of the air or fluid pushing the object forward, it pushes it to either side, over and over. This continual back and forth makes the whole structure shake back and forth ever more violently as behind it, the fluid forms a rather beautiful structure now dubbed the Karman Vortex Street.

This stuff was no joke — and even though Karman was lionized for figuring it out in 1911, the lesson didn’t always stick. The most famous example of the Karman Vortex Street taking something down was the Ferrybridge Power Station, a coal plant in England. Built in the 1950s, the plant managed to struggle along until November 1st, 1965, when winds of eighty-five miles per hour swept through the station. Three of the eight cylindrical cooling towers began to vibrate. They had been placed together so that between them they spun up the vortex, which pushed them all back and forth. In mid-morning, the three towers collapsed, leading to a fire that took out the other five.

Now bridge pilings, towers, airplanes, and other structures, are built with the vortex street very much in mind. Some are carefully proportioned, and some have ‘screw’ shapes cut into them to encourage the air to flow one way or another, but not both. You can still see Karman Vortex Streets forming behind planes, behind any pilings in water, and behind entire islands. The image just to the left of this paragraph is a street forming off Rishiri Island in Japan. Fortunately, the islands show no sign of toppling over.

Image credits: Fragile Oasis, ESA/The Map Addict and NASA.

(via scinerds)