A proof of concept numerical fluid dynamics simulation run with the AREPO moving mesh code. A solid, moving surface with reflective boundary conditions (the spoon) stirs a "cup of coffee" which is initially two different density fluids in equilibrium. The spoon motion and velocity is circular, and leads to mixing between the two phases and the development of billows and Kelvin-Helmholtz type instabilities.
Ideal fluid density is visualized with a volume rendering animation, where the transfer function illuminates the spoon in white, low density fluid is black, high density fluid is blue, and density fluctuations are highlighted by a series of narrow red and green Gaussians.
Video download and additional information available at: http://www.cfa.harvard.edu/~dnelson/