# Strouhal Number in Fluid Mechanics

**Formula:** `St = f * L / V`

The Strouhal number (St) is a dimensionless number that describes oscillating flow mechanisms. It is used to characterize the oscillatory behavior of the flow past bluff bodies and is defined as the ratio of the product of the frequency (f) of vortex shedding and the characteristic length (L) to the flow speed (V).

Mathematically, ** St = (f * L) / V**, where

**is the frequency of vortex shedding,**

*f***represents a characteristic length of the body (often diameter or hydraulic diameter), and**

*L***is the flow speed or velocity of the fluid.**

*V*This number helps predict the lock-in range of the vortex shedding frequency and the dynamic forces acting on the body. It is crucial in the study of flow-induced vibration and noise and is widely used in the design of chimneys, cables, and bridges to prevent aeroelastic phenomena such as galloping and vortex-induced vibrations.

Tags: Fluid Mechanics, Dimensionless Number, Flow, Vortex Shedding, Strouhal Number