Strouhal number

The Strouhal number is defined as follows:

w     velocity of flow around a body (for propellers, the relative velocity at the impeller outlet is used) in m/s
f      vortex-shedding frequency (sought excitation frequency) in s^-1
d     characteristic quantity of the separating vortices (thickness of profile surrounded by the flow) in m

The dimensionless number plays an important role in hydro-acoustics and characterises transient flow phenomena in all cyclically operating prime

Sr = 0.2 to 0.24 (flow along the plate)