vortex-streets

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Kármán Vortex Street - Digital visualization and Satellite Image

Kármán Vortex Street is a repeating pattern of swirling vortices caused by the unsteady separation of flow of a fluid around blunt bodies. 

The first image is a visualization of the vortex street behind a circular cylinder in are, the flow is made visible through release of oil vaopour in the air near the cylinder. 

The second image is a satellite image of a vortex street caused by wind flowing around the Juan Fernandez Islands of the Chilean coast.

The wake of a cylinder is a series of alternating vortices shed as the flow moves past. This distinctive pattern is known as a von Karman vortex street. The speed of the flow and the size of the cylinder determine how often vortices are shed. Incredibly, this pattern appears at scales ranging from the laboratory demo all the way to the wakes of islands. Von Karman vortex streets can even be seen from space. (Image credit: R. Gontijo and W. Cerqueira, source video)

Von Karman vortex streets are a pattern of alternating vortices shed in the wake of a bluff body. They’re commonly associated with cylinders and can be demonstrated in simulation and in the lab. (They even show up in supersonic flows.) But they also show up in nature quite frequently, like in this cloud pattern off Central America. Such wakes often occur downstream of rocky, volcanic islands that rise above the smooth ocean surface and disrupt the atmosphere’s boundary layer. The same phenomenon is responsible for the “singing” of electrical lines on a windy day, and I’ve even heard it make the spokes on my bicycle wheel sing in a crosswind. (Photo credit: R. Mastracchio; via @BadAstronomer; submitted by jshoer)

Von Karman Vortices Off Chile

Two small islands had a big impact on the skies over the Pacific Ocean in January 2013, creating paisley patterns that stretched 280 kilometers (175 miles). The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image on January 13, 2013.

The Juan Fernandez Islands are located roughly 800 kilometers (500 miles) off the Chilean coast. The biggest of these—Isla Alejandro (Alexander) Selkirk and Isla Robinson Crusoe—are volcanic islands situated along an east-west-trending submarine ridge. Each island boasts a tall summit. With an area of 52 square kilometers (20 square miles), Isla Alejandro Selkirk reaches an altitude of 1,650 meters (5,413 feet) above sea level. Slightly smaller, Isla Robinson Crusoe has a total area of 48 square kilometers (19 square miles), and reaches an altitude of 922 meters (3,025 feet).

The islands are tall enough to disturb air flow over the ocean. When an object such as an island interferes with the movement of air, von Karman vortices form in the air on the downwind (or leeward) side of the island. Also known as vortex streets, they are double rows of spiral eddies that are made visible by the clouds.