Vortex simulations modulated in a sphere.
The modulation field starts at 0.0 at the center,
and then increases to 1.0 at about 2/3's distance from
the center, then returns to 0.0 at the outer radiius.
The returned image is filtered by a Curl function
relative to the center point.
There are 4 versions 30 seconds long,
each with different starting conditions.