Strouhal number

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In dimensional analysis, the Strouhal number (St, or sometimes Sr to avoid the conflict with the Stanton number) is a dimensionless number describing oscillating flow mechanisms. The parameter is named after Vincenc Strouhal, a Czech physicist who experimented in 1878 with wires experiencing vortex shedding and singing in the wind. The Strouhal number is an integral part of the fundamentals of fluid mechanics. The Strouhal number is often given as St = f L U , {\displaystyle {\text{St}}={\frac {fL}{U}},} where f is the frequency of vortex shedding in Hertz, L is the characteristic length (for example, hydraulic diameter or airfoil thickness), and U is the average flow speed in meters per second. In certain cases, like heaving (plunging) flight, this characteristic length is the amplitude of oscillation....

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