Transition to Quantum Turbulence Generated by an Oscillating Object in Superfluid 4He

The transition to turbulence in boundary flow of superfluid 4He is investigated using a vibrating wire. An object in a superfluid is usually accompanied by remanent vortices, enabling to cause turbulence by its oscillation even at very low temperature. However, remanent vortices make it difficult to investigate the transition to turbulence. Recently, we have successfully devised a condition of a vortex-free superfluid, in which an oscillating object cannot generate turbulence. Using a “vortex-free” vibrating wire and a generator of vortex rings, we find that vortex rings can trigger the transition to turbulence for the vortexfree vibrating wire. This result indicates that vortex rings attach to the wire, being stretched and forming turbulence by its oscillation. The propagation time of trigger vortex rings, from their generation to a transition to turbulence for the vortex-free vibrating wire, is the order of 10 ms, suggesting the lower limit of vortex rings in size which enable to trigger the turbulent transition.