Turbulence in Pure Superfluid Flow

Free Decay of Superfluid Turbulence

“…Measured properties of superfluid turbulence in steadystate channel flow include the line-length density L, 1 the associated mutual friction force density F sn exerted by the superfluid on the normal fluid, [1][2][3][4][5] and the overall drift velocity (v t ) of the vortex tangle with respect to the superfluid. 6 Only the results for F^ can be thought of as well established, the previously accepted measurements of L by Vinen having recently been challenged, 7 while the single experiment determining {v t ) is subject to uncertainties in interpretation.…”

Steady and Decaying Flow of He II in a Channel with Ends Blocked by Superleaks

“…As for thermally induced pure superflow of He II, to the best of our knowledge the turbulent state characterized by L 1=2 Tv ÿ v I cr -state A-is the only one so far experimentally observed [3,5,14]. Here we report the discovery of a new state B, characterized by the linear dependence L v ÿ v II cr .…”

“…We confirm the existence of a weakly temperature dependent critical velocity v I cr of order 1 cm=s [14], which does not scale with the channel size and is therefore an intrinsic property of the selfsustained vortex tangle. In addition to the previously reported turbulent state A characterized by L 1=2 T v ÿ v I cr [5], we have discovered a new state B characterized by L v ÿ v II cr , where seems temperature independent. It poses an important question about why the quadratic generation mechanism, so well established in thermal counterflow, ceases to work.…”

“…Our data agree with the early calculations by Schwarz [4] for steady homogeneous counterflow, predicting a weakly temperature dependent v I cr of about 1 cm=s. Historically, this prediction was first thought to contradict the experimental observation of pure superflow by Tough's group [5], both in circular (id 0:13 mm) and rectangular (0:057 0:57 mm 2 ) cross sections, where no evidence of v I cr was found. Only later careful experiments in a circular (id 0:13 mm) tube confirmed the finite and nearly temperature independent value v I cr , of about 1:5 cm=s [14] (see Fig.…”

“…Starting with the He II counterflow experiments and the phenomenological theory of Vinen [2], via the subsequent experimental investigations of several groups, in particular, by Tough's group [3], and thanks to theoretical and computing efforts, especially by Schwarz [4], a fair level of understanding was achieved and in the 1980s, experiments on thermally induced He II turbulence were effectively terminated. However, puzzles such as the existence of two turbulent states in counterflowing He II denoted by Tough [3] as TI and TII as opposed to only one observed in pure superflow [5] or the anomalous decay of counterflow turbulence [2,6] remained. Moreover, in most early studies QT was created in counterflowing He II, which has no classical counterpart, so it seemed reasonable to think that classical and QT were different in character.…”