Froude number
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In fluid dynamics, the Froude number (named after William Froude) is the reciprocal of the square root of the Richardson number.
It is sometimes called Reech-Froude number after Ferdinand Reech, who introduced it for testing ships and propellers in 1852. Also, a number of other French researchers used this number before Froude.
the Froude number is defined as
- <math>
u\over\sqrt{gh} <math> where <math>u<math> is a representative speed, g the acceleration due to gravity, and <math>h<math> a representative length scale.
When used in the context of the Boussinesq approximation it is defined as
- <math> {u\over \sqrt{g' h}}<math>
where g' the reduced gravity (see Boussinesq approximation) and <math>h<math> a representative vertical lengthscale. Strictly, this is known as the densimetric Froude number.
The densimetric Froude number is usually preferred by modellers who wish to nondimensionalize a speed preference to the Richardson number which is more commonly encountered when considering stratified shear layers.
For example, the leading edge of a gravity current moves with a front Froude number of about unity.de:Froude-Zahl nl:Getal van Froude fi:Frouden luku