Helium II thermal counterflow at large heat currents: Profound effects of geometry

Ladner, D. R.; Tough, J. T.

doi:10.1103/physrevb.17.1455

Cited by 18 publications

(3 citation statements)

References 4 publications

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“…If the aspect ratio of the channel is high, the counterflow exhibits Fig. 2 Typical temperature and pressure difference ∆T and ∆p as a function of heat current Q for a circular flow tube at 1.7 K with thermal counterflow [26]. The broken line is an extrapolation of the linear region, consistent with Eq.…”

Section: Two-fluid Model and Thermal Counterflowsupporting

confidence: 62%

Numerical Studies of Quantum Turbulence

2017

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We review numerical studies of quantum turbulence. Quantum turbulence is currently one of the most important problems in low temperature physics and is actively studied for superfluid helium and atomic Bose-Einstein condensates. A key aspect of quantum turbulence is the dynamics of condensates and quantized vortices. The dynamics of quantized vortices in superfluid helium are described by the vortex filament model, while the dynamics of condensates are described by the Gross-Pitaevskii model. Both of these models are nonlinear, and the quantum turbulent states of interest are far from equilibrium. Hence, numerical studies have been indispensable for studying quantum turbulence. In fact, numerical studies have contributed in revealing the various problems of quantum turbulence. This article reviews the recent developments in numerical studies of quantum turbulence. We start with the motivation and the basics of quantum turbulence and invite readers to the frontier of this research. Though there are many important topics in the quantum turbulence of superfluid helium, this article focuses on inhomogeneous quantum turbulence in a channel, which has been motivated by recent visualization experiments. Atomic Bose-Einstein condensates are a modern issue in quantum turbulence, and this article reviews a variety of topics in the quantum turbulence of condensates e.g. two-dimensional quantum turbulence, weak wave turbulence, turbulence in a spinor condensate, etc., some of which has not been addressed in superfluid helium and paves the novel way for quantum turbulence researches. Finally we discuss open problems.

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Section: Two-fluid Model and Thermal Counterflowsupporting

confidence: 62%

Numerical Studies of Quantum Turbulence

2017

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“…In Fig. 2, the critical Reynolds Re s = V c d/κ with κ being the quantum of circulation of 4 He is displayed for the datasets reported in ten papers published over a period of 25 years between 1960 and 1985 [25][26][27][28][29][30][31][32][33][34]. The datasets have been partitioned into three temperature ranges to better evidence a possible temperature dependence.…”

Section: A Critical Velocities In Superfluid Counterflowsmentioning

confidence: 99%

Disproportionate entrance length in superfluid flows and the puzzle of counterflow instabilities

2017

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Systematic simulations of the two-fluid model of superfluid helium (He-II) encompassing the Hall-Vinen-Bekharevich-Khalatnikov (HVBK) mutual coupling have been performed in two-dimensional pipe counterflows between 1.3 and 1.96 K. The numerical scheme relies on the lattice Boltzmann method. A Boussinesq-like hypothesis is introduced to omit temperature variations along the pipe. In return, the thermomechanical forcings of the normal and superfuid components are fueled by a pressure term related to their mass-density variations under an approximation of weak compressibility. This modeling framework reproduces the essential features of a thermally driven counterflow. A generalized definition of the entrance length is introduced to suitably compare entry effects (of different nature) at opposite ends of the pipe. This definition is related to the excess of pressure loss with respect to the developed Poiseuille-flow solution. At the heated end of the pipe, it is found that the entrance length for the normal fluid follows a classical law and increases linearly with the Reynolds number. At the cooled end, the entrance length for the superfluid is enhanced as compared to the normal fluid by up to one order of magnitude. At this end, the normal fluid flows into the cooling bath of He-II and produces large-scale superfluid vortical motions in the bath that partly re-enter the pipe along its sidewalls before being damped by mutual friction. In the superfluid entry region, the resulting frictional coupling in the superfluid boundary layer distorts the velocity profiles toward tail flattening for the normal fluid and tail raising for the superfluid. Eventually, a simple analytical model of entry effects allows us to re-examine the long-debated thresholds of T 1 and T 2 instabilities in superfluid counterflows. Inconsistencies in the T 1 thresholds reported since the 1960s disappear if an aspect-ratio criterion based on our modeling is used to discard data sets with the strongest entry effects. Furthermore, it is observed that entry effects can spuriously reproduce the signature of a T 2 transition with a normal flow remaining laminar.

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“…Different experiments conducted with a broad range of channel dimensions and over a broad temperature range have shown that in helium II three distinct turbulent states exist [36,37]. Two of the turbulent states called TI and TII occur in round and small aspect ratio channels whereas a third turbulent regime named TIII occurs in wide aspect ratio channels.…”

Section: Quantum Turbulence In Helium IImentioning

confidence: 99%

Helium II heat transfer in LHC magnets : polyimide cable insulation

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Helium II thermal counterflow at large heat currents: Profound effects of geometry

Cited by 18 publications

References 4 publications

Numerical Studies of Quantum Turbulence

Numerical Studies of Quantum Turbulence

Disproportionate entrance length in superfluid flows and the puzzle of counterflow instabilities

Helium II heat transfer in LHC magnets : polyimide cable insulation

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