Stereoscopic visualization study of turbulence and vortex-tangle dynamics in He II

Non-Technical Abstract:

When liquid helium is cooled to below about -271 degrees Celsius, it becomes a superfluid (called He II), which can do things that other fluids cannot, such as flowing through a narrow capillary without apparent friction and climbing over container walls despite the gravity. The fascinating hydrodynamics of He II has many important applications. For instance, it supports an extremely efficient heat-transport mode called thermal counterflow and therefore has been widely utilized as a coolant material in scientific instruments.

When stirred, He II can also create vortex tubes which are essentially tiny tornadoes with thin hollow cores. Understanding the dynamics of a tangle of vortex tubes can benefit the study of various physical systems such as neutron stars that consist of neutron-pair superfluid. In this project, the research team aims to explore some predicted anomalous behaviors in counterflow turbulence and to visualize the vortex tubes in He II using advanced three-dimensional flow visualization techniques.

This research can produce fundamental knowledge indispensable for better applications of He II. The research team consists of both postdoctoral researchers and graduate students. Through the project, the team members are expected to gain valuable knowledge in fluid dynamics, cryogenics, and laser technologies.

The skills they learn through the research training are also crucial for their success in today's job market. In addition, the research team plans to conduct educational demonstrations involving cryogenic fluids in various outreach programs at the National High Magnetic Field Laboratory. The PI is also committed to serve the research community by organizing workshop and conferences to engage junior researchers.

Technical Abstract:

The current research work consists of: 1) a stereoscopic molecular tagging velocimetry (MTV) study of the anomalous anisotropy in He II counterflow turbulence, and 2) an exploration of the vortex tangle dynamics using a scanning particle tracking velocimetry (PTV) method. The stereoscopic MTV system, which incorporates a unique double-line optical setup, is developed as the first-of-its-kind equipment in quantum turbulence research.

It offers the capability of making unambiguous measurements of the normal-fluid velocity field and its spatial correlations in the coupled two-fluid system, which breaks the ground for solving various challenging problems. The study of the anomalous anisotropy in He II counterflow turbulence is expected to produce experimental data that are critical for the development of a complete theoretical understanding of this complex doubly turbulent system.

Such an understanding not only advances the knowledge of turbulence in general but also aids the cryogenic engineers in designing more efficient He II based cooling systems. The scanning PTV system to be developed enables real-time imaging of quantized vortex tangles in three-dimensional space, which offers a great opportunity for vortex research that is not possible otherwise.

The planned research on exploring the vortex-reconnection scaling, vortex-velocity correlations, and vortex trajectory statistics should produce important new knowledge needed for the development of an advanced statistical model of quantum turbulence.

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.