Vortices are found across a wide range of spatial scales and environments, including the water spiraling down a bathtub drain and the whirlpools of cooling plasma that sink into the Sun’s interior. To create a vortex in the lab, a tank of water is typically mounted on a rotating table. The water drain is aligned with the rotation axis, and a vortex appears and remains above the drain. Natural vortices, however, typically follow a more complicated motion.
To model that more realistic situation, Rick Munro (University of Nottingham, UK) and Mike Foster (the Ohio State University) set up a closed cylindrical tank with the drain located at its midradius, filled it with water, and rotated it at an angular velocity of 0.6 rad/s. A vortex initially forms over the drain but quickly moves off by self-induction and follows a more-or-less circular path around the axis until it finally comes to...
