The vortex shedding frequency is the vibrating frequency of the vortex shedding. It is the frequency which is directly proportional to the velocity of the liquid flowing in the pipe, and hence to volumetric flow rate. It is independent of fluid properties such as density, viscosity, conductivity, etc., except that the flow must be turbulent for vortex shedding to occur.
The basic relationship between vortex shedding frequency and fluid velocity is given below:
St = f(d/V)
In the above equation, St represents the Strouhal number which is a typical dimensionless calibration factor used to differentiate a variety of bluff bodies.
Other parameters are
F = vortex shedding frequency
d = width of the bluff body
V = average fluid velocity.
The Strouhal number is generally defined as the ratio of the interval between vortex shedding (l) and width of the bluff body (d). If the Strouhal number of two different bluff bodies is equal, then they will work in the same manner.