In fluid mechanics, the Roshko number (Ro) is a dimensionless number describing oscillating flow mechanisms. It is named after the American Professor of Aeronautics Anatol Roshko. It is defined as



where
- St is the dimensionless Strouhal number;
- Re is the Reynolds number;
- U is mean stream velocity;
- f is the frequency of vortex shedding;
- L is the characteristic length (for example hydraulic diameter);
- ν is the kinematic viscosity of the fluid.
Correlations
Roshko determined the correlation below from experiments on the flow of air around circular cylinders over range Re=50 to Re=2000:
valid over [ 50 <= Re < 200]
valid over [200 <= Re < 2000]
Ormières and Provansal investigated vortex shedding in the wake of a sphere and found a relationship between Re and Ro in the range 280 < Re < 360.