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MENTAL MODEL · M4932

Strouhal Number

Strouhal Number
TechnicalHigh supportFluid Mechanics
Included
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Version 1.0.0 · Updated 2026-07-30

CORE DEFINITION

A dimensionless number describing the frequency of wake oscillation behind an object in a fluid. Surprisingly, for almost all efficiently swimming or flying animals (dolphins, sharks, birds), the Strouhal number converges to a range of 0.2-0.4. This is the 'rhythm' with the highest propulsive efficiency.

SCAFFOLDING EFFECT

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Finding the optimal rhythm. In work or exercise, one should not only focus on the action (posture) but also on the 'frequency'. There exists a universal, physically most efficient rhythm range; too fast (waste) or too slow (stall) leads to inefficiency.

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The dimensionless number St = fL/U characterizes the relationship between vortex shedding frequency, flow velocity, and characteristic length in unsteady flows, used to describe phenomena such as the Kármán vortex street. It is a similarity criterion in fluid mechanics.

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Source support: Explicit

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    en.wikipedia.orghttps://en.wikipedia.org/wiki/Strouhal_numberZH · Explicit
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