Transition from Dissipationless Superflow to Homogeneous Superfluid Turbulence

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

“…Our observation of v I cr in two channels of sizes almost 2 orders of magnitude wider agrees within the error bars with that of Ref. [14] and shows that for pure superflow (or via Galilean transformation also for homogeneous counterflow) Re s scaling does not hold and v I cr is indeed an intrinsic property of a self-sustaining tangle, in accord with the early considerations and calculations of Schwarz [4].…”

“…However, it was assumed that (as in thermal counterflow [3]) v I cr scales with the size of the channel d, and in Ref. [14] the results are given in the dimensionless form of a ''superfluid Reynolds number'' Re s v I cr d=. Our observation of v I cr in two channels of sizes almost 2 orders of magnitude wider agrees within the error bars with that of Ref.…”

“…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.…”

“…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. 3).…”

“…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 .…”