Strouhal number#
Named after: Vincenc Strouhal (1850-1922).
$$\text{St} \stackrel{\text{def}}{=} \frac{f L}{U} \sim \frac{\text{oscillation speed}}{\text{flow speed}}$$
Description#
Measures oscillation time scale relative to advective flow time scale. It connects periodic motion such as vortex shedding to the speed and size of the flow.
Quantities#
| Name | Symbol | SI units | Dimension |
|---|---|---|---|
| frequency | \(f\) | \(\mathrm{Hz}\) | \(\text T^{-1}\) |
| characteristic length | \(L\) | \(\mathrm{m}\) | \(\text L\) |
| velocity | \(U\) | \(\mathrm{m}\,\mathrm{s}^{-1}\) | \(\text L\,\text T^{-1}\) |
Regimes#
Fluid oscillations
| Range | Regime | Description |
|---|---|---|
| 0 – 0.1 | low | Oscillations are rapidly swept by the fast flow. |
| 0.1 – 1 | intermediate/shedding | Periodic vortex shedding patterns. |
| 1 – ∞ | high | Localized oscillations dominate the flow. The fluid vibrates or pulsates in place. |