In dimensional analysis, the Strouhal number is a dimensionless number describing oscillating flow mechanisms. Often, it is given as
where Sr is the Strouhal number, f is the frequency of vortex shedding, D is the hydraulic diameter of the object in the fluid flow and V is the velocity of the fluid.
The Strouhal number is a function of the Reynolds number Re and in the region 200<Re<200,000 it is assumed to be equal to 0.2.
