Image by Ole Myrtroeen and Gary Hunt.
This vortex looks so friendly, we made it our image of the week! It was formed in a physical experiment in which a saline solution (stained blue) was ejected upwards into a still fresh-water environment. The image was produced by Ole Myrtroeen and Gary Hunt, University of Cambridge, and appeared on the cover of vol. 657 of Journal of Fluid Mechanics, © Cambridge University Press.
The picture is one of the images that appears in the book 50 visions of mathematics, which celebrates the 50th anniversary of the Institute of Mathematics and its Applications.
You can see previous images of the week here.