Study on the turbulent flow of superfluid<sup>4</sup>He generated by a vibrating wire
Yano H., Handa A., Nakagawa M., Obara K., Ishikawa O., Hata T.
We have studied the flow of superfluid4He generated by a vibrating wire. As the drive force increases, the velocity of the wire grows in the laminar-flow regime, until it suddenly drops at the onset of the turbulent-flow regime. As the drive force decreases, the turbulence disappears at a critical velocity. This result suggests that the vortices on the wire are confined within a finite size, even in turbulence. We have measured the critical velocity of seven vibrating wires, whose resonance frequencies range from 0.5 kHz to 9 kHz, at 1.4 K and found that the critical velocity is almost constant below an oscillation frequency of 2 kHz and increases above this frequency. We have also observed the response of a vibrating wire in superfluid4He at a low temperature of 30 mK. We find that the resonance frequency jumps upward at the same moment as the entry of the flow to a turbulent state. The frequency jump may be caused by vortex dynamics such as expansion, entanglement, and reconnection occurring in the turbulence. © 2006 American Institute of Physics.