Wu number

The Wu number (${\displaystyle Wu}$) is a nondimensional quantity in fluid mechanics describing the effects of rotating axisymmetric bodies on wall-bounded sheer flows. The parameter is named after the Chinese scientist Yongxiang Wu during his work on boundary layer instabilities.

DefinitionEdit

The Wu number is defined as.^[1]

${\displaystyle Wu={\frac {\omega D}{2u_{k}}}}$,

where ${\displaystyle \omega }$ is the circular frequency, ${\displaystyle D}$ the diameter of the axisymmetric body (like for instance a cylinder) and ${\displaystyle u_{k}}$ the local flow velocity at the top of the body. It is therefore the ratio of the velocities of the body edge and the surrounding flow.

ApplicationsEdit

Rotating bodies on boundary layers are a means of active flow control on wings, empennage or stabilizers on airplanes. For large Wu numbers (), the instability mechanisms are governed by the rotation of the body. For small Wu numbers () the stability-related effects of the body itself may outweigh its rotatory effects 

This article uses material from the Wikipedia article  Metasyntactic variable, which is released under the  Creative Commons Attribution-ShareAlike 3.0 Unported License.