Vortex Shedding on a Car
Vortex shedding describes a flow of a fluid past a bluff (not a streamlined structure) body at defined velocities. The vortices are depending on the size and shape of the body, the fluid and the velocity. In a flowing fluid, vortices are created in the lee side of the body.
If the body creates a periodic alternating vortices, these are forming a Von Kármán vortex street. This effect creates alternating high- and low-pressure zones behind the structure which can lead to noise, vibrations and altering forces which also can move the object creating the vortices.
The video shows a simplified simulation of a Porsche 356 1600 convertible cruising at 100 km/h in turbulence free air. The windshield can be seen as the bluff, mentioned above. The created vortex will not lead to a von Kalman vortex street because the ground will reflect the upper vortex and will also work as a barrier. However, the transient and non-steady behaviour is visible. The low pressure within the vortex will drag the car to the rear and increases the cw-value or drag coefficient.