Text: http://en.wikipedia.org/wiki/Vortical In fluid dynamics, the movement of a fluid can be said to be vortical if the fluid moves around in a circle, or in a helix, or if it tends to spin around some axis. Such motion can also be called solenoidal. Vortical movement is characterized by non-zero curl: \nabla \times \mathbf{v} \ne 0 i.e. \operatorname{curl}\ \mathbf{v} \ne 0, where v is the velocity vector field of the fluid. The curl of the velocity (at a specified point of the vector field) yields a vector which points in the direction around which the fluid is rotating. See also: vortex, vorticity.

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