 # Vorticity facts for kids

Kids Encyclopedia Facts

Vorticity is a mathematical concept used in fluid dynamics. It can be related to the amount of "circulation" or "rotation" (or more strictly, the local angular rate of rotation) in a fluid.

The average vorticity in a small region of fluid flow is equal to the circulation $\Gamma$ around the boundary of the small region, divided by the area A of the small region. $\omega_{av} = \frac {\Gamma}{A}$

Notionally, the vorticity at a point in a fluid is the limit as the area of the small region of fluid approaches zero at the point: $\omega = \frac {d \Gamma}{dA}$

Mathematically, the vorticity at a point is a vector and is defined as the curl of the velocity: $\vec \omega = \vec \nabla \times \vec v .$

One of the base assumptions of the potential flow assumption is that the vorticity $\omega$ is zero almost everywhere, except in a boundary layer or a stream-surface immediately bounding a boundary layer.

Because a vortex is a region of concentrated vorticity, the non-zero vorticity in these specific regions can be modelled with vortices.

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