Cats2D Multiphysics > Developments > Supercalifragilistic

Supercalifragilisticexpialidocius

Unmixing of colored particles in a lid-driven cavity, with left and right boundaries translating in opposite directions. This flow has a saddle streamline that separates flow into a pair of co-rotating vortexes around which an outer flow recirculates. The initial condition is obtained by mixing the fluid for 50 dimensionless time units. Four spiral arms, two on each side of the cavity, form each time unit, so this is quite a long time with much mixing. Then the flow is reversed (it's Stokes flow, so it's physical). Watch it unmix by mousing over the images:

The same situation mixed for only 5 time units and played back at one-tenth the speed:

Only with Cats2D.