Jack Dodd Centre for Quantum Technology, Department of Physics, University of Otago, Dunedin 9016, New Zealand.
Joint Quantum Centre (JQC) Durham-Newcastle, Department of Physics, Durham University, Durham DH1 3LE, United Kingdom.
Phys Rev Lett. 2015 Apr 17;114(15):155302. doi: 10.1103/PhysRevLett.114.155302. Epub 2015 Apr 16.
The Reynolds number provides a characterization of the transition to turbulent flow, with wide application in classical fluid dynamics. Identifying such a parameter in superfluid systems is challenging due to their fundamentally inviscid nature. Performing a systematic study of superfluid cylinder wakes in two dimensions, we observe dynamical similarity of the frequency of vortex shedding by a cylindrical obstacle. The universality of the turbulent wake dynamics is revealed by expressing shedding frequencies in terms of an appropriately defined superfluid Reynolds number, Re(s), that accounts for the breakdown of superfluid flow through quantum vortex shedding. For large obstacles, the dimensionless shedding frequency exhibits a universal form that is well-fitted by a classical empirical relation. In this regime the transition to turbulence occurs at Re(s)≈0.7, irrespective of obstacle width.
雷诺数提供了对向湍流转变的特征描述，在经典流体动力学中有广泛的应用。由于超流体的本质上是无粘性的，因此在超流体系统中识别这样的参数具有挑战性。通过对二维超流圆柱尾流进行系统研究，我们观察到圆柱障碍物的涡旋脱落频率具有动力学相似性。通过用适当定义的超流体雷诺数 Re(s) 来表示脱落频率，揭示了湍流尾流动力学的普遍性，该雷诺数考虑了量子涡旋脱落导致的超流流动的破裂。对于大障碍物，无量纲脱落频率表现出一种通用形式，很好地符合经典经验关系。在这个范围内，无论障碍物宽度如何，向湍流的转变都发生在 Re(s)≈0.7 处。
