Cloud streets flowing south across Bristol Bay hit the Shishaldin and Pavlof volcanoes, which part the air flow into distinctive swirls called von Karman vortex streets. As air flows around the volcano, a vortex is shed first on one side, then the other. Although the usual example for this type of flow is the wake of a cylinder, vortex streets can extend behind any non-aerodynamic body immersed in a flow. The same phenomenon is responsible for the singing of power lines in the wind. As astronaut Dan Burbank observes, “It’s classic aerodynamics, but on a thousands of miles scale.” (Photo credit: Dan Burbank, NASA)
Tag: von Karman
Vortex Shedding
Whenever a bluff (i.e. non-aerodynamic) body is placed in a flow of sufficient Reynolds number, it will shed periodic vortices, creating a pattern known as a von Karman vortex street. The animation above shows the phenomenon in the wake of a cylinder, but vortex streets form behind many other bodies as well, including islands. Each vortex shed causes forces on the body and alternating vortices can cause the body to vibrate. This is what causes suspended power lines to “sing” in the wind. #
