The vorticity
of a velocity vector field
is its curl,
. It measures the local rotation of the field. For
a two-dimensional vector field
, vorticity is commonly represented by the scalar
field
.
For a smooth solution of the three-dimensional incompressible Euler equations without external forcing, vorticity satisfies
|
(1)
| |||
|
(2)
|
The right side is the vorticity-stretching term. It vanishes for two-dimensional incompressible flow. The Beale-Kato-Majda criterion (Beale et al. 1984) relates finite-time breakdown of a smooth three-dimensional Euler solution to a time integral of the maximum vorticity.