Turbulence is all around us. It’s in the swirl of coffee and milk in a latte, unfurling along the wings of airplanes and the sides of cars, churning the blood in your heart after the valve snaps closed. Yet we still don’t fully grasp all of its rules.
Part of the challenge is that physicists typically start by isolating the phenomenon from its environment to study it – but stirring a cup means the spoon is always still inside it, affecting the movement of the liquid. There hasn’t been a way to separate the turbulence out by itself.
A group of University of Chicago scientists, however, have pioneered a way to create contained turbulence in a tank of water. They use a ring of jets to blow loops until an isolated “ball” of turbulence forms and lingers.
“It was a surprise to us,” said physicist Takumi Matsuzawa, the first author on a study describing the findings, published in Nature Physics. “It’d be like calmly sitting in a field with a picnic and watching a storm raging 50 feet away,” said Prof. William Irvine, the corresponding author on the study.
They hope the breakthrough opens a new avenue of study to better understand turbulence.
‘No one knew this was even possible’
Turbulence—the chaotic flow in an unevenly mixed substance—is an old problem. “It’s often quoted as one of the big open questions in physics,” said Irvine.
In the past decades, scientists have made progress in describing the behavior of an “idealized” state of turbulence. That is, turbulence without confounding variables like boundaries, or variations in strength and time. But when it comes to real-world turbulence, there is much left to understand.
“Turbulence appears everywhere around us, but it keeps eluding what physicists consider a satisfying description,” said Irvine. “For example, if you ask, can I predict what happens next when I poke this region of turbulence? The answer is no. Not even really with a supercomputer.”
One of the big problems was the presence of confounding variables in experiments. You can make turbulence by shooting a fast jet of water through a pipe or by stirring a paddle in a tank of water, but the turbulence is always brushing up against the container walls and the stirrer, which affects the results.
Matsuzawa, Irvine, and their collaborators had been running experiments with tanks of water to make “vortex rings” – like smoke rings, but in water. When they tried to combine them to make turbulence, the energy usually bounced right back at them before dissipating.
—Prof. Chuan He
