This is the result of a numerical calculation in fluid dynamics, illustrating the increasing complexity of the whirls caused by an object moving through a fluid. In this case, we start with a body moving in fluid at uniform speed, creating a free sinusoidal wake which can be modeled by a suitably perturbed vortex sheet. As time progresses (going down in the figure) the vortex sheet shows increasingly winding spirals.
Computational fluid dynamics is becoming increasingly important in simulations of many big projects; it allows to "test" how changes in the shape or geometry of an object (an airplane, a combustion nozzle, ..) will affect its functionality without having to construct many different prototypes.
Figure credit: Robert Krasny.
URL for this and other pictures of computations related with fluid mechanics: http://www.math.lsa.umich.edu/~krasny/picture_gallery.html
Two other sites with (colorful!) Computational Fluid Dynamics pictures and movies: http://www.math.rug.nl/~veldman/cfd-gallery.html and the "Gallery" at http://ctr.stanford.edu/