Boundary layer separation and vortex creation in superflow through small orifices

We report on numerical solutions of the Gross-Pitaevskii equation for two-dimensional flow of a super fluid condensate through a small orifice. When the superfluid velocity in the center of the orifice exceeds about 60% of the speed of sound, the flow in the throat of the orifice becomes unstable to a form of boundary layer separation. Low condensate-density regions bulge away from the walls and form the cores of singly quantized vortices. These detach from the boundary and are convected downstream.