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# Strouhal Number

## Introduction to the Strouhal Number

The Strouhal Number is a dimensionless value useful for analyzing oscillating unsteady fluid flow dynamics problems.

The Strouhal Number can be expressed as

St = ω l / v                                             (1)

where

St = Strouhal Number

ω = oscillation frequency

l = characteristic length

v = flow velocity

The Strouhal Number can be important when analyzing unsteady, oscillating flow problems. The Strouhal Number represents a measure of the ratio of the inertial forces due to the unsteadiness of the flow or local acceleration to the inertial forces due to changes in velocity from one point to an other in the flow field.

The vortices observed behind a stone in a river, or measured behind the obstruction in a vortex flow meter, illustrates these principles.

## Related Topics

• ### Fluid Mechanics

The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.

## Related Documents

• ### Dimensionless Numbers

Physical and chemical dimensionless quantities - Reynolds number, Euler, Nusselt, and Prandtl number - and many more.
• ### Technical Terms in Fluid Mechanics

Some commonly used technical terms in fluid mechanics.
• ### Vortex Flowmeters

An introduction to vortex flowmeters.
• ### Vortex Flowmeters - Shedding Frequency vs. Volume Flow Rate

The vortex shedding frequency created around a bluff body and flow rate.

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6.3.17

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