The operating principle of the vortex meter is based on the fact that when a flow hits an obstruction (bluff body), it separates and moves around the object to continue on down stream. Vortex swirls separate from the object on alternating sides at the contacting point with the object. This shedding causes low pressure swirls on one side and high pressure on the other side. The process is reversed from one side to another and keeps on alternating. The two swirl frequencies are 180 degrees out of phase to each other. And the frequency of this shedding process is proportional to the velocity of the flow.
By measuring the frequency of formation of the vortex on any side of the bluff body, the flow rate can be obtained. The fluid velocity is proportional to the vortex frequency and the width of the bluff body.
All the factors are known in these two equations except the frequency of vortex formation and the flow rate. Therefore, by measuring the frequency, the flow rate can be calculated using the equation.
The vortex meter works well on relatively clean liquids, gas, and steam that do not contain a significant amount of solids. Attention should be paid when dealing with gases having low densities because it generates weak pressure pulses and therefore the signal may be hard to detect.