Numerous physics studies have been conducted on turbulence, a fluid motion characterized by chaotic changes in flow velocity and pressure. Despite the fact that turbulence is a natural phenomenon that occurs frequently, controlling its properties and manipulating it have so far proven extremely challenging.
A new method for consistently controlling the location, position, and properties of turbulence in experimental settings was recently developed by researchers at the University of Chicago. They were able to create an isolated turbulent blob in a calm environment using this method, which was presented in a paper that was published in Nature Physics.
“Everywhere there is turbulence.” A good example is to stir coffee with a spoon,” Takumi Matsuzawa, the study’s first author, and William Irvine, the study’s corresponding author, told Phys.org. However, compared to the other conventional phases of matter, such as liquid and solid, manipulating this ephemeral phase of matter is more difficult. Similar to the spoon in the previous illustration, the material boundaries frequently conceal what the turbulence has been feeding. We wondered if it was possible to create an isolated blob of turbulence and keep it there because of this.
“Our proposed method entails constructing turbulence by placing eddies one at a time, much like Legos. Nobody knows exactly what an eddy is, but a vortex ring, also known as a smoke ring, is a suitable candidate because it is a strong fluid structure that can travel well beyond the material bounds. Furthermore, its properties can be fully measured, allowing us to know exactly what we are feeding into turbulence.”
William Irvine
Irvine and his colleagues set out to create a restricted state of turbulence within a still environment as part of their most recent research. This would require precise control over the properties of turbulence. Physicists may be able to investigate questions that have been challenging to answer through conventional experimental methods if it is possible to successfully create such an isolated blob. This would open up intriguing new research avenues.
“The following are some of the questions that could be investigated following our study: What transpires between non-turbulent and turbulent flows at their interface? How are conserved quantities like impulse and energy moved across the interface? What kinds of turbulence exist in relation to the combinations of conserved quantities?” According to Irvine and Matsuzawa,
Turbulence is depicted as a soup of “eddies”—swirling motions—in numerous physics textbooks and theoretical works. Although the specific characteristics of eddies remain a mystery, they are basically fluid movements that deviate from the flow of the fluid, like circular currents or vortices.
Irvine explained, “Our proposed method entails building turbulence by placing eddies one at a time, like Legos.” A vortex ring, also known as a smoke ring, is a good candidate for an eddy because it has a strong fluid structure that can travel far beyond material boundaries. Furthermore, its entire properties can be measured, enabling us to determine what we feed into turbulence.”
Matsuzawa combined sets of eight vortex rings in a chamber by firing them from each of the eight corners toward the center of a cubic, water-filled tank. Vortex reconnections would cause these vortex rings to split and reorient themselves if they were fired as a single set. However, the researchers’ method of repeatedly firing them results in the formation of a single turbulence blob.
According to Irvine, “Our approach provides unique design principles for localizing, positioning, and controlling turbulence.” The vortex rings determine the blob’s characteristics; The ring radius determines the size; and the energy carried by the rings determines the level of inner turbulence. Other conserved quantities, such as angular impulse and helicity, whose roles in turbulence are unknown, may also be injected if helical loops are combined.
This group of researchers’ most recent work makes a significant contribution to the study of turbulence by introducing a promising method for consistently controlling it experimentally. The approach they describe in their paper may open the door to future studies that would have been challenging to carry out otherwise. This could, in turn, contribute to the resolution of long-standing research queries regarding the physical processes that are the foundation of turbulence.
Irvine continued, “We are currently investigating how turbulence freely evolves in a quiet environment.” This is a crucial inquiry into how turbulent fluctuations spread and fade. Additionally, we are interested in figuring out how turbulence “forgets” what it has fed into it. Even if the vortical structures in the input are different, it is believed that there is universal turbulence at the small scale. By combining various vortex loops and tuning the input, our system would be ideal for studying this memory in turbulence.”
More information: Takumi Matsuzawa et al, Creation of an isolated turbulent blob fed by vortex rings, Nature Physics (2023). DOI: 10.1038/s41567-023-02052-0
