This Number Keeps Bridges Safe from Wind!
Named after the Czech engineer Vincenc Strouhal, the Strouhal number (St) represents the ratio of the unsteady flow's characteristic frequency (f) to the product of the velocity (V) and a characteristic length (L) of the flow.
Formula: St = f * L / V.
A Strouhal number less than 1 implies a low-frequency flow, where the periodicity of the flow structures is relatively long compared to the characteristic length and velocity, often observed in slow or steady flows.
A Strouhal number around 0.2 to 0.3 indicates the shedding of vortices behind a bluff body or an obstacle, such as in the wake of a cylinder, where the periodic shedding of vortices occurs at a characteristic frequency relative to the flow velocity and the size of the body.
A Strouhal number greater than 1 implies a high-frequency flow, where the periodicity of the flow structures is relatively short compared to the characteristic length and velocity, often observed in fast or turbulent flows.
The Strouhal number is commonly used to characterize vortex shedding and wake dynamics behind bodies in fluid flows, aiding in the understanding of phenomena such as vortex streets and the generation of noise in flow around objects.
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