超流体氦-4中的非经典壁面律
A nonclassical law of the wall in superfluid helium-4
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中文总结 AI 辅助
该研究探究超流体氦-4的近壁流动，通过实验发现其正常流体速度仍符合壁面律，但有效卡门常数远小于经典值，揭示经典湍流壁面律在量子流体中的转变，为低温冷却系统设计提供指导。
中文摘要 AI 辅助
经典湍流中最稳健的尺度律之一是壁面对数律，但它是否能在超流体氦-4（He II）这类量子流体中存在仍未知。在固体壁面处，He II的粘性正常流体分量与无粘超流体分量遵循完全不同的边界条件，不过它们的运动可通过量子化涡旋耦合。这些竞争效应如何组织近壁流动是量子流体动力学中的开放问题。本研究采用分子标记测速技术，对雷诺数达1.26×10^6的机械驱动He II管流的近壁速度场进行可视化，并通过压降测量独立确定壁面剪切应力。研究发现，正常流体速度呈现稳健的对数分布，表明尽管He II具有双流体特性，壁面律描述依然存在；但显著的是，所得壁面律明显非经典：有效卡门常数小于经典值的一半，且在所研究的温度范围内几乎保持不变。尽管双流体分量的相对占比发生了显著变化，这种不变性表明两者间存在强动力学耦合。这些结果不仅揭示了经典湍流的普适律如何被量子流体动力学改造，还为涉及He II输运的低温冷却系统的设计与运行提供了重要指导。
英文摘要
The logarithmic law of the wall is one of the most robust scaling laws of classical turbulence, yet whether it survives in a quantum fluid such as superfluid $^4$He (He II) remains unknown. At a solid wall, the viscous normal-fluid and inviscid superfluid components of He II obey fundamentally different boundary conditions, yet their motions can be coupled through quantized vortices. How these competing effects organize the near-wall flow remains an open question in quantum-fluid hydrodynamics. Here we visualize the near-wall velocity field in mechanically driven He II pipe flows at Reynolds numbers up to $1.26\times10^6$ using molecular tagging velocimetry and independently determine the wall shear stress from pressure-drop measurements. We find that the normal-fluid velocity develops a robust logarithmic profile, showing that a law-of-the-wall description persists despite the two-fluid nature of He II. Strikingly, however, the resulting wall law is distinctly nonclassical: the effective Kármán constant is less than half its classical value and remains nearly unchanged across the temperature range studied. This invariance, despite substantial changes in the relative fractions of the two components, indicates strong dynamical coupling between them. These results not only reveal how a universal law of classical turbulence is transformed by quantum hydrodynamics, but also provide valuable guidance for the design and operation of cryogenic cooling systems involving He II transport.
发表机构
- National High Magnetic Field Laboratory（国家强磁场实验室）
- Florida State University（佛罗里达州立大学）
机构由 AI 辅助整理，请以论文原文为准。
