When is it useful?
Strouhal number scales a repeating flow frequency by speed and length. It is used to compare vortex shedding behind a cylinder or other periodic flow across different sizes and speeds.
Formula and inputs
Enter the frequency f in Hz, characteristic length L in m, and flow speed v in m/s. For cylinder vortex shedding, the cylinder diameter is a common choice for L. Record what physical signal produced f before comparing results.
Open this calculatorWorked example
If the shedding frequency is f = 10 Hz, cylinder diameter L = 0.1 m, and flow speed v = 5 m/s, then St = 10 × 0.1 ÷ 5 = 0.2.
Interpreting the result
The result expresses frequency relative to the flow-through time scale. Comparisons with other experiments require a consistent geometry and frequency measurement.
Limits and cautions
A zero flow speed makes this formula undefined. A zero or unrelated frequency also needs reconsideration before the result can describe a periodic flow.
Formula and concept reference: NASA Glenn — Laminar Flow Over a Cylinder. We created the sample inputs and calculations for this guide.