Steady and stable physical phenomena are seldom interesting to me. Instabilities, though, generate dynamics that depend strongly on the type and details of the situation. When two fluids of different densities are in contact, but the lighter fluid is beneath the heavier fluid, you have what is called a Rayleigh-Taylor Instability. The interface between the two fluids will begin to deform at the slightest provocation. In this case, I begin the fluids with a large sinusoidal perturbation. In doing so, I force the initial large-scale dynamics into a predictable pattern. But because I have turned diffusion down to a nearly-negligible level, the ensuing motions spin off levels and smaller levels of detailed wisps, eddies, and swirls. The drawback of this very low diffusion is that the computer simulation becomes unstable near the end---watch out for the numerical noise in the final few seconds.
"Sinurti 7b" is 4200 Frames from a two-dimensional Rayleigh-Taylor Instability run at Reynolds number 100M on a 4.1k x 2.3k uniform grid. The frames were reduced to 1080p for this video.