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Quantum turbulence of bellows-driven ~4He superflow: Decay

机译：波纹管驱动的量子湍流〜4He超流：衰减

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We report on studies of quantum turbulence with second sound in superfluid ~4He in which the turbulence is generated by the flow of the superfluid component through a wide square channel, the ends of which are plugged with sintered silver superleaks, the flow being generated by compression of a bellows. The superleaks ensure that there is no net flow of the normal fluid. In an earlier paper [S. Babuin et al., Phys. Rev. B 86, 134515 (2012)] we have shown that steady flow of this kind generates a density of vortex lines that is essentially identical to that generated by thermal counterflow, when the average relative velocity between the two fluids is the same. In this paper we report on studies of the temporal decay of the vortex-line density, observed when the bellows is stopped, and we compare the results with those obtained from the temporal decay of thermal counterflow remeasured in the same channel and under the same conditions. In both cases there is an initial fast decay which, for low enough initial line density, approaches for a short time the form t~(-1) characteristic of the decay of a random vortex tangle. This is followed at late times by a slower t~(-3/2) decay, characteristic of the decay of large "quasiclassical" eddies. However, in the range of investigated parameters, we observe always in the case of thermal counterflow, and only in a few cases of high steady-state velocity in superflow, an intermediate regime in which the decay either does not proceed monotonically with time or passes through a point of inflexion. This difference, established firmly by our experiments, might represent one essential ingredient for the full theoretical understanding of counterflow turbulence.
机译：我们报道了关于超流体〜4He中具有第二种声音的量子湍流的研究，其中湍流是由超流体成分通过一个宽的方形通道的流动而产生的，该流动的端部被烧结的银超泄漏物堵塞，该流动由压缩产生波纹管。超级泄漏确保正常流体没有净流量。在较早的论文中[S. Babuin等人，物理学。 Rev. B 86，134515（2012）]我们已经表明，当两种流体之间的平均相对速度相同时，这种稳定流会产生与热逆流产生的涡流密度基本相同的密度。在本文中，我们报告了在波纹管停止时观察到的涡流线密度随时间衰减的研究，并将结果与​​在相同通道和相同条件下重新测量的热逆流随时间衰减获得的结果进行了比较。 。在这两种情况下，都有一个初始快速衰减，对于足够低的初始线密度，它会在短时间内接近随机涡旋缠结的衰减特征形式t〜（-1）。随后是较晚的t〜（-3/2）衰减，这是大型“准经典”涡旋衰减的特征。但是，在研究的参数范围内，我们总是在热逆流的情况下观察到，并且仅在少数情况下在超流中具有较高的稳态速度时，这种中间状态下衰减要么不会随时间单调进行，要么不会通过通过拐点。通过我们的实验确定的这种差异可能代表了对逆流湍流的完整理论理解的一个基本要素。

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  • 来源
    《Physical review》 |2015年第18期|184503.1-184503.13|共13页
  • 作者

    S. Babuin; E. Varga; W. F. Vinen; L. Skrbek;

  • 作者单位

    Institute of Physics ASCR, Na Slovance 2, 182 21 Prague, Czech Republic;

    Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague, Czech Republic;

    School of Physics and Astronomy, University of Birmingham, Birmingham BI5 2TT, United Kingdom;

    Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague, Czech Republic;

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