Flow Visualization Study of Quantum Hydrodynamics in Superfluid Helium-4

点击翻译按钮获取中文摘要

When liquid helium is cooled to about -271 degrees Celsius, it becomes an inviscid superfluid and can do things that other fluids cannot, such as seeping through ultra-thin cracks and climbing over container walls. The fascinating hydrodynamics of superfluid helium has many important scientific and engineering applications. For instance, it supports the most efficient heat-transport mechanism as a coolant material, and it also allows the generation of violent turbulent flows in compact laboratory equipment for model testing of airplanes and ships. However, the lack of quantitative flow measurement tools in this cold fluid has impeded progress in understanding and utilizing its hydrodynamics. In this project, the research team aims to elucidate the nature of emergent properties of various turbulent flows in superfluid helium by employing a newly developed molecular-tagging flow visualization technique. This research is expected to produce fundamental knowledge indispensable for better applications of superfluid helium. The research team is composed of graduate and undergraduate students. These students can gain experience in fluid dynamics, cryogenics, and advanced laser technologies. These skills give the students the technical dexterity necessary to excel in today's science- and technology-dominated market. In addition, the research team plans to conduct demonstrations involving superfluid helium in various educational and outreach programs at the National High Magnetic Field Laboratory to introduce profound scientific concepts to the general public.The objective of the research work is to apply a newly developed molecular tagging velocimetry (MTV) technique to tackle outstanding problems in two forms of flows in superfluid helium: thermal counterflow that can be produced by an applied heat current and quasiclassical flow that can be generated via mechanical forcing. Preliminary study on counterflow in the principle investigator's lab has revealed a novel form of turbulence. Understanding this turbulence is now regarded as one of the most challenging problems in quantum turbulence research. Using the MTV technique, the research team plans to conduct systematic study on how the energy spectrum of the counterflow turbulence may vary with heat flux in a wide range of temperatures. This information can form the base for the development of a theoretical understanding of the intriguing counterflow turbulence. In the experiment on studying towed-grid generated quasiclassical turbulence, flow visualization is combined with second sound attenuation method for probing the motion of the two fluid components in superfluid helium. The research team plans to examine the two-fluid coupling model and measure emergent flow properties that cannot be reliably determined in the past. This work is expected to pave the way for various exciting applications of superfluid helium in future turbulence research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.