COUNTERFLOW-INDUCED MACROSCOPIC VORTEX RINGS IN SUPERFLUID-HELIUM - VISUALIZATION AND NUMERICAL-SIMULATION

The existence of macroscopic vortex rings produced without any moving mechanical part, simply by releasing a heat pulse of appropriate inten sity and duration at the closed end of a circular counterflow channel, will be proved. From consecutive pictures, taken from a light sheet c rossing the axis of symmetry, the formation and further propagation of the vortex rings can be studied. The average translational velocity a s well as the vortex parameters like ring and core diameter are compar ed with the observations found for vortex rings generated by a moving piston. Due to the interaction of superfluid and normal fluid turbulen ce the counterflow-induced vortex rings are turbulent and appear unsta ble. The experimental observations are compared with numerical simulat ions where the boundary conditions for the normal fluid and the superf luid velocity have been chosen appropriately.