Vortex shedding von Karman effect flow measurement.
A vortex flowmeter makes use of the von Karman effect principle where vortices are created downstream from a bluff body or shedder bar. A sensor is mounted in an optimum position behind the bluff body obstruction where the vortices are created and measures the oscillation generated in the flow. The resulting frequency measured is directly proportional to the flow velocity.
Vortices are created when a fluid flows around an obstruction. As the fluid closest to the obstruction passes around the shedding obstruction it will speed up, and the pressure will drop. This effect diminishes as you move further away from the boundary layer where the fluid meets the obstruction.
As fluid flow increases the vortices grow in size and eventually will begin to detach from the boundary layer creating alternating whirlpools on either side of the shedder. The alternating whirlpools cause pressure fluctuations to develop, as low and high pressure pockets pass by the sensor.
Since the vortex shedding occurs at repeatable intervals, the sensor will convert the resulting increase and decrease in pressure to a frequency signal.
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