Tying smoke rings in a knot

Structures similar to smoke rings that are linked and twisted are reported for the first time online this week in Nature Physics.

Mixing or sudden turbulence in a fluid can induce a rotational motion known as a vortex. A common example of this is the ring exhaled by a smoker, which is a vortex folded back on itself to create a closed loop. Understanding the fluid dynamics of such vortices helps meteorologists predict unusual atmospheric effects, for instance. However, laboratory-based studies have been limited only to very simple rings. Dustin Kleckner and William Irvine now create and image linked rings and vortices tied into knots using a 3D-printed hydrofoil passing through water.

“Such vortices appear in a surprisingly large range of phenomena including superconductors, superfluids and the plasmas found in the solar corona and the Earth’s magnetosphere,” says Daniel Lathrop in an accompanying News and Views article. The ability to recreate intricate vortices therefore enables modelling of a diverse range of real-world systems.