In fluid dynamics, a Kármán vortex street (or a von Kármán vortex sheet) is a repeating pattern of swirling vortices caused by the unsteady separation of flow of a fluid around blunt bodies. It is named after the engineer and fluid dynamicist Theodore von Kármán. In low turbulence, tall buildings can produce a Kármán street so long as the structure is uniform along its height. In urban areas where there are many other tall structures nearby, the turbulence produced by these prevents the formation of coherent vortices. Periodic crosswind forces set up by vortices along object’s sides can be highly undesirable, and hence it is important for engineers to account for the possible effects of vortex shedding when designing a wide range of structures, from submarine periscopes to industrial chimneys and skyscrapers.

I modeled here a classical problem of the flow around cylinder. I’ve done it in SolidWorks to see its functionality in terms of fluid mechanics.

This phenomena can be observed in different ranges of Reynolds number, for example, I took Re = 100 in this case which is between 90 and 150 where vortex street can be observed behind cylinder.
In nature you can see this phenomenon everywhere. I noticed it once in the park. Vortex street behind a stone:

 

 

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