Physicists at the University of Chicago and applied mathematicians at the Flatiron Institute recently carried out a study exploring the behavior of viscous fluids in which tiny rotating particles were suspended, acting as local, mobile sources of vorticity. Their paper, published in Nature Physics, outlines fluid behaviors that were never observed before, characterized by self-propulsion, flocking and the emergence of chiral active phases.

"This experiment was a confluence of three curiosities," William T.M. Irvine, a corresponding author of the paper, told Phys.org. "We had been studying and engineering parity-breaking meta-fluids with fundamentally new properties in 2D and were interested to see how a three-dimensional analog would behave.

"At the same time, we were interested in building active matter at intermediate Reynolds numbers to see what new behaviors inertia would give rise to, and finally, we had been playing with building turbulence by combining vortex loops and were interested if it could be done by combining 'point' vortices."

To carry out their experiments, Irvine and his colleagues first created a large number of cylindrical millimeter-sized particles. They then used magnetic fields to drive these particles to spin while suspended in a viscous fluid.

They observed that individual particles generated a localized three-dimensional region of vorticity around it. This swirling region, which they dubbed a "vortlet," produced various fascinating fluid behaviors.