Fluid Knots and Smoke Ring Physics
You can create your own smoke rings at home with this cool science experiment, but scientists waited over a century for experimental evidence of an elusive twist on this fluid flow: knotted vortex loops.
Earlier this year, scientists from the University of Chicago gathered that long-sought data with the help of a 3-D printer, lasers, and a high-speed camera. This month, those same scientists, headed by postdoctoral researcher Dustin Kleckner, released an updated video explaining the physics behind these beautiful, twisted fluid flows.
To observe the knotted loops, the research team first used a 3-D printer to create special hydrofoils tied in knots. Next, they accelerated the hydrofoils through a fluid to imprint the knotted structure onto the fluid, generating the vortex knots that they sought. Lasers and a high-speed camera tracked the knots as they twisted and morphed, giving the researchers a 3-D timelapse of the evolving fluid flow.
In the research team's video entry (embedded below) for the 2013 Gallery of Fluid Motion, you can see the beautiful images the team captured during their research.
As shown in the second half of the video, the originally knotted loops can quickly stretch and untie themselves — a fact that initially surprised the researchers. In an ideal fluid, these knotted loops are supposed to remain stable. The real world, however, is far from ideal. One originally knotted loop, for instance, stretched, disentangled and re-connected as two distinct, un-linked loops in a fraction of a second.
The researchers hope to branch out from this investigation into other types of fluids to see how universal this instability is. The "re-connections," seen after the knots unravel may also shed light on interactions found outside of fluid dynamics, such as magnetic field lines. You can find the researchers' brief paper describing this video on the arXiv.
Last week, we told you about another entry ("Fluid Juggling") to this year's Gallery of Fluid Motion — an annual contest hosted by the American Physical Society's Division of Fluid Dynamics (DFD).
You can search and download other video entries on arXiv.org. Just search for "Gallery of Fluid Motion 2013," click on a paper, and look to the right under "Ancillary Files." For papers that have video entries, there should be links to low quality and high quality downloads. Winners for the Gallery of Fluid Motion will be announced during DFD's annual meeting in late November.
Or you can create your own vortex rings here: http://physicscentral.com/experiment/physicsathome/cannon.cfm
Friday, October 25, 2013 at 1:11 AM