Published: Tuesday, March 12, 2013

Knotty Fluid

Vortex gets tied in knots

A knotted plastic wing like this one, created with a 3-D printer, allowed physicists to generate linked vortex rings.

A knotted plastic wing like this one, created with a 3-D printer, allowed physicists to generate linked vortex rings.

Swirling rings of fluid have for the first time been tied in a knot. Physicists accomplished the feat with the help of some unlikely lab tools: YouTube videos of dolphins and a 3-D printer.
β€œIt’s a remarkable experiment,” says Carlo Barenghi, a mathematician and physicist at Newcastle University in England. The creation of these knotted vortices in the lab, reported online March 3 in Nature Physics, could help scientists understand the flow of plasma on the sun and the flow of air, blood, and other fluids here on Earth, Barenghi says.
A vortex is a swirling mass of fluid, such as a tornado or a whirlpool within a cup of coffee after stirring in milk. Vortices can also bend and warp into various configurations; the most familiar example is a smoke ring, a twisted cylinder of circulating smoke particles.
In 1867, Scottish physicist Lord Kelvin went a step further and suggested that vortex rings could tie in knots. His idea didn’t get much traction at first, but throughout the 20th century, mathematicians and physicists offered evidence that knotted vortex loops could emerge in various fluids and plasmas and affect their flow. More recently, in January astronomers spotted braided rings of plasma generated by the sun’s magnetic field in the solar corona.

Source: Science News