When a heavier fluid sits atop a lighter one, the interface between them can be unstable. This means that even a very slight disturbance will be enough to cause fingers of dense (dark) fluid to sink while fingers of the lighter (white) fluid rise. This is known as the Rayleigh-Taylor instability, and it’s responsible for all kinds of beautiful patterns in our daily lives, like the mixing of cream in ice coffee. It can cause cell-like patterns in acrylic painting, umbrella-like forms in ink drops, and finger-shaped protrusions in a nebula. It’s an important force in supernovas and a major challenge in achieving fusion.
The fundamental feature that connects all of these examples is the acceleration of a lighter fluid into a heavier one. For many of them that acceleration is simply the force of gravity, but as with the supernova and nebula, other forces can be responsible for the acceleration. The instability also looks a little different depending on the geometry. The simulation in this post shows a 2D example of the Rayleigh-Taylor instability; three-dimensional versions often look more like umbrellas or mushrooms. (Video and image credit: C. van Heerwaaden)
Leave a Reply