Strouhal Number

Strouhal number, abbreviated as St, a dimensionless number, is used in fluid dynamics to describe the relationship between the frequency of vortex shedding behind a bluff body and the flow velocity.  It is the ratio of inertial forces due to the unsteadiness of the flow or acceleration of inertial forces due to the changes in velocity between points in a flow field.

The Strouhal number provides information about the oscillating nature of the flow.  It is commonly used in the study of fluid dynamics, aerodynamics, and hydrodynamics, particularly in relation to flow induced vibrations and vortex shedding behind structures such as cylinders, airfoils, or chimneys.  The Strouhal number can help engineers and scientists understand and predict the behavior of fluid flow around these structures.

 

Strouhal number formula
\( Sr \;=\; f \; l_c \;/\;v \)     (Strouhal Number) \( f \;=\; Sr \; v\;/\;l_c \) \( l_c \;=\; Sr \; v\;/\;f \) \( v \;=\; f \; l_c\;/\;Sr \)
Symbol	English	Metric
\( St \) = Strouhal number	\(dimensionless\)	\(dimensionless\)
\( f \) = frequency of vortex shedding	\(dimensionless\)	\(dimensionless\)
\( l_c \) = characteristic length	\(ft\)	\(m\)
\( v \) = flow velocity	\(ft\;/\;sec\)	\(m\;/\;s\)