Strouhal number

A criterion for the similarity of non-stationary motions of liquids or gases. The Strouhal number characterizes the identity of the flow of the processes in the course of time:

$$\mathrm{Sh}=\frac{l}{vt}=\frac{\omega l}{v},$$

where $v$ is the typical velocity of the flow, $l$ is the typical linear dimension, $t$ is the typical period of time for non-stationary motion, and $\omega$ is the typical frequency (the inverse quantity $vt/l$ is sometimes also denoted by Sh).

The same criterion $H_0=vt/l$ in mechanical, thermal and electromagnetic processes is called the homochromity test.

The Strouhal number is named after V. Strouhal.

References

[a1]	L.I. Sedov, "Similarity and dimensional methods in mechanics" , Acad. Press (1959) (Translated from Russian)