ring of vorticity

Two-dimensional simulation of a ring of vorticity (color-filled contours).
Stream function (dashed white contours) is calculated from vorticity with a direct solution of the Poisson equation.
Velocity is calculated from the stream function. A third-order upwind scheme is used to advect vorticity.
Computation with Python and numpy.
1025×1025 grid points
The initial ring is set slightly off-center so that the perturbation is not purely a wave number 4.

hope this works!