An ordering transition in the turbulent flow of helium II

Abstract

We report the observation of some remarkable features in the flow of a vertical, planar jet of superfluid helium forced through a macroscopic orifice while carrying heat. We observed a transition from a state in which the profile of the free surface of the jet carried a Kelvin-like wave to a state with an almost undisturbed interface. This transition was observed as a heat flux in the jet stream was increased. This new state presented a bifurcation of the stream at the orifice such that a second branch coursed through a narrow stream into a hydraulic jump to the side of the jet and orifice. The hydraulic jump exhibited sharply periodic surface waves travelling away from the orifice. The stream velocities and heat currents for which this new state was observed greatly exceeded the critical velocity¹ and the critical heat current² for the onset of quantum turbulence. This sudden transition into a less chaotic steady-flow configuration above velocities large enough to induce shearing instabilities in a stream has no precedent in the hydrodynamics of ordinary fluids and is a phenomenon which has not been previously observed in superfluid helium.