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:
is the velocity vector field of the fluid.
The curl of the velocity (at a specified point of the vector field) yields a vector (or actually a pseudo-vector) which points in the direction around which the fluid is rotating. In this way it is similar to the eigenvector of a rotation matrix.
See also: vortex, vorticity.