A team of researchers from the University of Chicago has developed a novel technique to generate contained turbulence in a water tank. They blow loops using a ring of jets until an isolated “ball” of turbulence develops and persists.
Scientists were surprised to find this. They now believe their breakthrough could pave the way towards a better understanding turbulence.
Turbulence is often considered as one of the big open questions in physics. Scientists have made progress in understanding the behavior of an “idealized” state of turbulence in recent decades. That is turbulence without ambiguous elements like boundaries or variations in intensity over time. But there is still a lot to learn about turbulence in the real world.
Confounding variables in experiments were one of the major issues. If you stir a paddle in a tank of water or blast a fast jet of water through a pipe, you can create turbulence, but the results will be impacted by the turbulence’s constant contact with the stirrer and container walls.
Water tanks had been the subject of research by Matsuzawa, Irvine, and their associates to create “vortex rings”—smoke rings in the form of rings of water. The energy typically bounced back at them when they attempted to combine them to create turbulence before vanishing.
But once they hit upon a particular configuration, something odd happened. When they repeatedly fired rings that met in the center, they watched as a ball of turbulence formed that was self-contained – away from the tank’s walls.
Physicist Takumi Matsuzawa, the first study author, said, “No one knew this was even possible. Turbulence is very good at mixing things; mixing your milk into your coffee can only get one or two swirls in before it becomes completely mixed. The fact we can contain it in place is very surprising.”
“A freestanding ball of turbulence allows scientists to track its parameters more precisely using lasers and multiple fast cameras. This includes its energy and its helicity (a measure of how tangled or “knotty” the loops are) as well as the impulse and angular impulse (the fluid equivalent of momentum and angular momentum).”
They could also experiment with it by changing the parameters. They could send in loops with helices spinning either clockwise or anticlockwise. They might alter the energy input, stop adding rings and watch the turbulence disappear, change the helicity of the rings, or see how the turbulence changed over time by changing the amount of energy going in.