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The repeated collision of eight vortices forms isolated turbulence. (Left) Decomposition of the clump energy into mean flow (yellow) and fluctuating (blue) components shows the formation of trapped turbulence. (Right) Highly irregular trajectories of trace particles are seen inside the turbulent patch. Credit: Matsuzawa et al

Turbulence, fluid motion characterized by chaotic changes in flow velocity and pressure, has been the subject of countless physics studies. Although turbulence is a very common phenomenon that occurs in nature, it has so far proved incredibly challenging to manipulate it and control its properties.

Researchers at the University of Chicago recently introduced a new strategy to reliably control the location, location, and properties of turbulence in experimental settings. This policy, presented in an article published in The physics of natureallowed them to create an isolated turbulence blob in a quiet environment.

“Turbulence is everywhere. Stirring coffee with a spoon is a good example,” Takumi Matsuzawa (first author of the study) and William Irvine (corresponding author of the study) told “Nevertheless, it is not as easy to treat this short-lived phase of matter as the traditional phase of matter like solid and liquid. In many cases, the matter boundary, like the spoon in the previous example, obscures any turbulence that has been given. This led to that we wondered if it was possible to create isolated turbulence and hold it in place.”

As part of their recent study, Irvine and his colleagues decided to create a finite state of turbulence in a quiescent environment, which would require precise control of the turbulence’s properties. The successful creation of such an isolated clump could open up interesting new avenues of research, allowing physicists to explore questions that have been difficult to answer with traditional experimental methods.

“Some of the questions that could be explored as a result of our research are: what happens at the interface between turbulent and turbulent flows? How are conserved quantities such as energy and momentum transferred across the interface? Are there different types of turbulence depending on the composition of conserved quantities?” said Irvine and Matsuzawa.

Many physics textbooks and academic works describe turbulence as a soup of swirling motions called “eddies.” Although the individual characteristics of eddies are rather uncontrollable, they are actually movements in a fluid that deviate from its general flow, such as eddies or eddies.

“Our proposed approach involves building up turbulence by stacking vortices one at a time, like Legos,” Irvine explained. “No one really knows what a vortex is, but a vortex ring, also called a smoke ring, is a good possibility, as it is a powerful fluid structure and can travel far from material boundaries. Moreover, its properties can be fully measured so we know what we feed into turmoil.”

In his experiments, Matsuzawa combined a set of eight rings into a chamber by shooting them toward the center of a water-filled tank from the eight corners. If these vortex rings were shot as a single set, they would split and redirect, due to an effect called vortex reconnection. Firing them repeatedly, as performed by the researchers, however, results in the formation of isolated turbulence.

“Our approach provides unique design principles to locate, localize and control turbulence,” said Irvine. “The properties of the clump are set by the vortex rings; the size is set by the ring radius; the internal turbulence intensity is set by the energy carried by the rings. If we combine spiral loops, we could also inject the conserved quantities such as angular momentum and helicity, but their roles in turbulence are not well known.”

Recent work by this group of researchers greatly contributes to the study of turbulence and introduces a promising strategy to reliably control it experimentally. In the future, the strategy presented in their paper could pave the way for new research that would have been difficult to carry out in the past. This in turn could help answer long-standing research questions related to the physical processes underlying turbulence.

“We are currently studying how turbulence develops freely in a quiet environment,” Irvine added. “This is an important question about how turbulent oscillations propagate and die out. We are also interested in studying how turbulence ‘forgets’ what has been fed. Turbulence is believed to be universal on the small scale, even if the eddy dynamics in the inlet are different. Our system would be ideal for studying this memory in turbulence by tuning the input by combining various vortex loops.”

More information:
Takumi Matsuzawa et al., Creation of an isolated turbulent mixture fed by vortex rings, The physics of nature (2023). DOI: 10.1038/s41567-023-02052-0

Diary information:
The physics of nature

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