# Strouhal number

﻿
Strouhal number

In dimensional analysis, the Strouhal number is a dimensionless number describing oscillating flow mechanisms. Often, it is given as:

:$mathrm\left\{Sr\right\}= \left\{f Lover v\right\}$

where $Sr$ is the dimensionless Strouhal number, $f$ is the frequency of vortex shedding, $L$ is the characteristic length (for example hydraulic diameter) and $v$ is the velocity of the fluid.

For spheres in uniform flow in the Reynolds number range of 800 < Re < 200,000 there co-exist two values of the Strouhal number. The lower frequency is attributed to the large-scale instability of the wake and is independent of the Reynolds number Re and is approximately equal to 0.2. The higher frequency Strouhal number is caused by small-scale instabilities from the separation of the shear layer (Kim and Durbin, 1988 and Sakamoto and Haniu, 1990).

The Strouhal number is named after Vincenc Strouhal and is an integral part of the fundamentals of fluid mechanics.

In Metrology, specifically axial-flow turbine meters, the Strouhal number is used in combination with the Roshko number to give a correlation between flow rate and frequency. The advantage of this method over the freq/viscosity versus K-factor method is that it takes into account temperature effects on the meter.

:$mathrm\left\{Sr\right\}= \left\{fover U\right\}\left\{C^3\right\}$

f = meter frequency,U = flow rate,C = linear coefficient of expansion for the meter housing material

This relationship leaves Strouhal unitless, although a unitless approximation is often used for C^3, resulting in units of pulses/volume (same as K-factor).

References

Kim, K. J. and Durbin, P. A. (1988) "Observations of the frequencies in a sphere wake and drag increase by acoustic excitation," Physics of Fluids, 31, pp. 3260-3265.

Sakamoto, H. and Haniu, H. (1990) "A study on vortex shedding from spheres in uniform flow," Journal of Fluids Engineering, 112(December), pp. 386-392.

* [http://www.weltderphysik.de/intern/upload/annalen_der_physik/1878/Band_241_216.pdf Vincenc Strouhal, Ueber eine besondere Art der Tonerregung]

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• Strouhal number — Strouhalo skaičius statusas T sritis fizika atitikmenys: angl. Strouhal number vok. Strouhalsche Zahl, f; Strouhal Zahl, f rus. число Струхаля, n pranc. nombre de Strouhal, m …   Fizikos terminų žodynas

• Strouhal number — Strouhalo skaičius statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas( ai) Grafinis formatas atitikmenys: angl. Strouhal number vok. Strouhalsche Zahl, f; Strouhal Zahl, f rus. число Струхаля, n pranc.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• Strouhal-Zahl — Strouhalo skaičius statusas T sritis fizika atitikmenys: angl. Strouhal number vok. Strouhalsche Zahl, f; Strouhal Zahl, f rus. число Струхаля, n pranc. nombre de Strouhal, m …   Fizikos terminų žodynas

• Strouhal-Zahl — Strouhalo skaičius statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas( ai) Grafinis formatas atitikmenys: angl. Strouhal number vok. Strouhalsche Zahl, f; Strouhal Zahl, f rus. число Струхаля, n pranc.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• Keulegan–Carpenter number — The Keulegan–Carpenter number is important for the computation of the wave forces on offshore platforms. In fluid dynamics, the Keulegan–Carpenter number, also called the period number, is a dimensionless quantity describing the relative… …   Wikipedia

• Vincenc Strouhal — (Čeněk Strouhal) (April 10, 1850 – January 26, 1922) was a Czech physicist specializing in experimental physics. He was one of the founders of the Physics department at Charles University. See also *Strouhal number Further reading *… …   Wikipedia

• Roshko number — In fluid mechanics, the Roshko number is a dimensionless number describing oscillating flow mechanisms. It is given as:: mathit{Ro} = {St} {Re} = {f L^{2}over u} where Ro is the dimensionless Roshko number, St is the dimensionless Strouhal number …   Wikipedia

• nombre de Strouhal — Strouhalo skaičius statusas T sritis fizika atitikmenys: angl. Strouhal number vok. Strouhalsche Zahl, f; Strouhal Zahl, f rus. число Струхаля, n pranc. nombre de Strouhal, m …   Fizikos terminų žodynas

• Womersley number — A Womersley number is a dimensionless number in biofluid mechanics. It is a dimensionless expression of the of pulsatile flow frequency in relation to viscous effects. It is named after John R. Womersley (1907 1958).The Womersley number, usually… …   Wikipedia

• Nusselt number — In heat transfer at a boundary (surface) within a fluid, the Nusselt number is the ratio of convective to conductive heat transfer across (normal to) the boundary. Named after Wilhelm Nusselt, it is a dimensionless number. The conductive… …   Wikipedia