Engineering researchers visualize the motion of vertebrae in superfluous turbulence

Nobel laureate in physics Richard Feynman once described turbulence as ‘the most important unsolved problem of classical physics’.

Turbulence in classical fluids such as water and air is difficult, in part because of the challenge of identifying the vortices in the fluids. The detection of vortex tubes and the detection of their motion can greatly simplify the modeling of turbulence.

But the challenge is easier in quantum fluids, which exist at low temperatures so that quantum mechanics – which deals with physics on the scale of atoms or subatomic particles – control their behavior.

In a new study published in Proceedings of the National Academy of Sciences, Florida researchers have succeeded in visualizing the vortex tubes in a quantum fluid, findings that may help researchers understand turbulence in quantum fluids and beyond.

“Our study is important not only because it broadens our understanding of turbulence in general, but also because it can be beneficial for the study of various physical systems that also include vortex tubes, such as superconductors and even neutron stars,” said Wei Guo. a co-worker, said. professor of mechanical engineering at the FAMU-FSU College of Engineering and the principal investigator of the study.

The research team studied superfluid helium-4, a quantum fluid that exists at extremely low temperatures and can flow forever in a narrow space without clear friction.

Guo’s team examined trace particles trapped in the vertebrae and observed for the first time that they move in the form of a vortex tube in a random pattern and move away from their starting point on average rapidly. It appears that the displacement of these trapped trackers increases much faster over time than in regular molecular diffusion – a process called superdiffusion.

By analyzing what happened, they discovered how the vortex velocities changed over time, which is important information for statistical modeling of quantum fluid turbulence.

“Superdistribution has been observed in many systems, such as cellular transport in biological systems and the search patterns of human hunter-gatherers,” Guo said. “A firm explanation of superdistribution for things that move randomly is that it sometimes has extraordinarily long displacements, known as Lévy flights.”

After analyzing their data, Guo’s team concluded that the super-distribution of the trackers in their experiment was not actually caused by Lévy flights. Something else is happening.

“We finally found that the superdistribution we observed was caused by the relationship between the vortex velocities at different times,” said Yuan Tang, a postdoctoral researcher at the National High Magnetic Field Laboratory and a paper author. . “The motion of each vortex segment initially appears to be random, but in fact the velocity of a segment was simultaneously positively correlated with its velocity at a subsequent time. This observation allowed us to make some hidden generic statistics. properties of a chaotic random vortex, which can be useful in various branches of physics. ‘

Unlike classical fluids, vortex tubes in superfluid helium-4 are stable and well-defined objects.

“They are essentially small tornadoes swirling in a chaotic storm, but with extremely thin hollow nuclei,” Tang said. “You can’t see them with the naked eye, not even with the strongest microscope.”

“To solve this, we did our experiments in the cryogenics laboratory, where we added trace particles in helium to visualize it,” said Shiran Bao, a postdoctoral researcher at the National High Magnetic Field Laboratory and an author. , added.

The researchers injected a mixture of deuterium gas and helium gas into the cold superfluid helium. After injection, the deuterium gas solidified and formed small ice particles, which the researchers used as the spores in the liquid.

“Just as tornadoes can suck nearby leaves into the air, our trackers can also be trapped in helium on the vortex tubes when they are near the tubes,” Guo said.

This visualization technique is not new and is used by scientists worldwide in research laboratories, but the breakthrough that these researchers made was to develop a new algorithm that enabled them to distinguish the detectors trapped in vortices from those who was not trapped.