Shear instability in a square box of 50 × 256 × 256 resolution with a perturbation of n = 5. Top-left: initial longitudinal velocity u. The other three frames are at t = 281, approximately 3.6 sound crossing times: top-right: passive tracer used to follow the locations of the 2 fluids; bottom-left: the longitudinal velocity u and bottom-right: latitudinal velocity v. These horizontal cuts are taken half-way up the computational domain.