Vortex evolution in a rotating tank with an off-axis drain

Fluid entering the periphery of a steadily rotating cylindrical tank exits through an off-axis drain hole, located in tank's base at half-radius. Experiments show that, though concentrated vortex forms over drain, it soon advects around what is first circular path. Though inviscid dynamics predicts continued motion, our experiments that moves inwards from predicted path, finally coming to rest approximately $50^{\circ }$ drain. In this final state, vorticity thin shear layer bounding irrotational core, which passes The broadening structure and eventual steady-state formation are believed be due growing boundary on outer wall.