Collaborative Research: Materials World Network: Collaborative Research on Simple Forms of Quantum Turbulence - Production, Decay and Visualization

经典流体中的湍流无论从理论角度还是在许多实际应用中都是重要的和具有挑战性的。这项研究是由佛罗里达大学、耶鲁大学与英国兰开斯特大学、曼彻斯特大学和伯明翰大学合作进行的，旨在了解经典湍流在超流体中是如何被修改的，例如液氦，在超流体中，流动受到与角动量量子化和完全缺乏粘性相关的量子条件的严格限制。量子湍流的特征取决于温度。就在超流体转变温度以下，超流体表现为正常(类经典)流体和超流体的混合物；两种流体中的一种或两种都可以是湍流的，这导致在低得多的温度下产生丰富多样的可能的湍流模式，只有超流体成分保留，最明显地展示了量子湍流的基本方面。如果能将湍流的模式可视化，将极大地促进量子湍流的研究。使用微米大小的氢颗粒作为示踪剂在其他地方已经是先驱，但该项目的研究人员正在实施使用亚稳态双原子氦分子形式的小得多的颗粒，这将通过激光荧光观察到。在略低于超流体转变的温度下，这些分子预计将跟随正常流体的运动，而在低得多的温度下，它们将跟随超流体成分中的量化涡旋运动。在这项工作的早期阶段，研究人员将开发这项技术，以便在更容易接触的温度范围内应用，在那里，分子可以追踪正常的流体，但量子湍流的许多重要方面仍需研究和理解。初步实验将为在较低温度下应用铺平道路。此外，由于在稳定移动的网格之后会产生一种非常简单的湍流形式，研究人员正在开发在非常低的温度下通过超流氦移动网格的技术，在这种情况下，量子湍流只涉及正常流体。由此产生的湍流将通过两种方式在全球范围内进行研究：观察由于湍流衰减而导致超流体升温的速率；以及使用离子散射来测量湍流涡旋浓度衰减的速率。拟议的实验的成功取决于佛罗里达(移动网格的发展及其背后的能量耗散研究)、耶鲁和曼彻斯特(可视化)、伯明翰(理论)、兰开斯特和曼彻斯特(移动网格后湍流涡旋集中的衰减)之间密切互动合作的发展。来自所有实验室的学生和博士后助理将在其他实验室工作，既促进整体努力，又进一步发展每个研究人员的能力-S。虽然这项工作由于低温环境而具有挑战性，但可能的回报是高的，因为对量子湍流的理解可能会提供对经典湍流的洞察，而到目前为止，经典湍流一直没有得到普遍的理解。

Turbulence in classical fluids is important and challenging both from a theory perspective and for many practical applications. This research, a collaboration between the University of Florida, Yale University, and the Universities of Lancaster, Manchester and Birmingham in the United Kingdom, aims to understand how classical turbulence is modified in a superfluid, such as liquid helium, in which flow is severely restricted by quantum conditions associated with the quantization of angular momentum and a complete lack of viscosity. Quantum turbulence has a character that depends on the temperature. Just below the superfluid transition temperature a superfluid behaves as a mixture of a normal (classical-like) fluid and a superfluid; either or both fluids can be turbulent, which gives rise to a rich variety of possible turbulent patterns At much lower temperatures only the superfluid component remains, exhibiting most clearly the fundamental aspects of quantum turbulence. The study of quantum turbulence would be greatly facilitated if the patterns of turbulent flow could be visualized. The use of micron-sized particles of hydrogen as tracers has been pioneered elsewhere, but the investigators in this project are implementing the use of much smaller particles in the form of metastable diatomic helium molecules, which will be observed by laser fluorescence. At temperatures somewhat below the superfluid transition such molecules are expected to follow the normal fluid, while at much lower temperatures they are expected to follow the quantized vortex motion in the superfluid component. In the earlier stages of the work the investigators will develop this technique for application in the more accessible temperature range where the molecules track the normal fluid, but where many important aspects of quantum turbulence have still to be studied and understood. The preliminary experiments will pave the way towards applications at lower temperatures. Also, since a very simple form of turbulence can be generated in the wake of a steadily moving grid, the investigators are developing techniques for moving a grid through superfluid helium at a very low temperature where the quantum turbulence involves only the normal fluid. The resulting turbulence will be studied on a global scale in two ways: observing the rate at which the superfluid heats up as a result of the decay of the turbulence; and using the scattering of ions to measure the rate at which the concentration of turbulent eddies decays. Success of the proposed experiments is dependent on the development of close interactive collaboration between Florida (development of the moving grid and study of energy dissipation behind it), Yale and Manchester (visualization), Birmingham (theory), Lancaster and Manchester (decay of the concentration of turbulent eddies behind a moving grid). Students and postdoctoral associates from all labs will work in the other labs both to promote the overall effort and further to develop each researcher?s capability. While the work is challenging because of the low temperature environment, the possible pay off is high, as an understanding of quantum turbulence may offer insights into classical turbulence which have heretofore escaped common understanding.