Vortex shedding von Karman effect flow metering instrumentation for measuring the flow velocity of a substance.
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 optimal 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 speed 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.
A flow velocity meter is category of device that is assigned to any instrument which can measure the speed of a substance passing through a specific location.
Flow velocity meters can provide an analogue, digital or pulse output of the flow speed.
If the diameter or cross sectional area of the flow is known, then the volume flow rate can be calculated from the flow velocity.
Secondary readings such as pressure, temperature, density and viscosity, may also be measured or entered into the device to allow the mass flow rate to be determined or to carry out enhanced flow calculations.
Some flow velocity meters include additional instrumentation to manipulate the flow reading and provide other functions such as the total quantity indication, or alarms each time a batch has been completed.