Abstract

We visualize the streaming flow due to a rapidly oscillating quartz tuning fork, in both normal He I and superfluid He II, by following the flow-induced motions of relatively small particles suspended in the liquid. Over the investigated temperature range, between 1.2 and 2.3 K, at the experimentally probed length scales, the streaming patterns observed in He II appear identical to those seen in He I and are very similar to those reported to occur in water, outside the Stokes boundary layer. The outcome strongly supports the view that, at scales larger than the quantum length scale of the flow, the mean distance between quantized vortices, mechanically forced turbulent coflows of He II behave classically, due to the dynamical locking of the two components of superfluid He4 by the action of the mutual friction force.