The evolution of semicircular quantum vortex loops in oscillating potential flow emerging from an aperture is simulated in some highly symmetrical cases. As the frequency of potential flow oscillation increases, vortex loops that are evolving so as eventually to cross all of the streamlines of potential flow are drawn back toward the aperture when the flow reverses. As a result, the escape size of the vortex loops, and hence the net energy transferred from potential flow to vortex flow in such 2π phase-slip events, decreases as the oscillation frequency increases. Above some aperture-dependent and flow-dependent threshold frequency, vortex loops are drawn back into the aperture. Simulations are performed using both radial potential flow and oblate-spheroidal potential flow.
Bibliographical noteFunding Information:
We would like to acknowledge the major contribution of C. L. Zim-mermann, who wrote the original code for the oblate-spheroidal potential flow simulations. This work was supported by the National Science Foundation under grants DMR 90-02890, 94-03522, and 96-31703, and by Luther College and the University of Minnesota – Morris, where many of the simulations by the first two authors were run. The University of Minnesota’s UROP program is also gratefully acknowledged.
- Oblate-spheroidal flow
- Oscillatory aperture flow
- Phase slip
- Superfluid He