The saturation of decaying counterflow turbulence in helium II

We are concerned with the problem of the decay of a tangle of quantized vortices in He II generated by a heat current. Direct application of Vinen's equation yields the temporal scaling of vortex line density $L \sim t^{-1}$. Schwarz and Rozen [Phys. Rev. Lett. {\bf 66}, 1898 (1991); Phys. Rev. B {\bf 44}, 7563 (1991)] observed a faster decay followed by a slower decay. More recently, Skrbek and collaborators [Phys. Rev. E {\bf 67}, 047302 (2003)] found an initial transient followed by the same classical $t^{-3/2}$ scaling observed in the decay of grid-generated turbulence. We present a simple theoretical model which, we argue, contains the essential physical ingredients, and accounts for these apparently contradictory results.Comment: 19 pages, 5 figure

Vibrating grid as a tool for studying the flow of pure He II and its transition to turbulence

We report a detailed experimental study of the flow of isotopically-pure He II, generated by a vibrating grid. Our measurements span a wide range of temperatures (50 mK < T < 1.37 K) and pressures (2 bar < p < 15 bar). The response of the grid was found to be of a Lorentzian form up to a sharply-defined threshold value. This threshold value does not change appreciably with pressure; the form of the resonant response of the grid is qualitatively the same for all temperatures while the threshold value is a monotonically increasing function of temperature. We discuss the measured variation of the resonant frequency of the grid as a function of applied pressure (density) of He II and relate this to a hydrodynamic effective mass of the grid. These measurements extend our previously reported studies [Nichol et al, Phys. Rev. E 70, 056307 (2004)] and form an integral part of a series of experiments aimed at providing a better understanding of classical and quantum turbulence