These images from a numerical simulation of a mixing layer between fluids of different density show the development and breakdown to Kelvin-Helmholtz waves. The black fluid is 3 times denser than the white fluid, and, as the two layers shear past one another, billow-like waves form (Fig 1(a)). Inside those billows, secondary and even tertiary billows form (Fig 1(a) and (b)). Fig 1 (c)-(e) show successive closeups on these waves, showing their beautiful fractal-like structure. (Photo credit: J. Fontane et al, 2008 Gallery of Fluid Motion) #
Fractal Fluids

Shawn
https://www.youtube.com/watch?v=iOOQaE0WR2I
check it out starting at frame position 2:25
Shawn Harrison
Can the Kelvin-Helmholtz instability happen in an arched or a circular vortex street like that?
Shawn Harrison
Periodicity in Kelvin-Helmholtz instabilities in smaller self-similar scales