Flow past a cylinder computed with an implementation of Stam’s Stable Fluids algorithm after ∼3 vertical fluid velocity crossing times on a 500 × 2000 zone grid. Color corresponds to the density (or concentration, given that ﹩{\boldsymbol{\nabla }}\cdot {\boldsymbol{v}}=0﹩) of passively advected dye that is injected into the flow upstream of the cylinder. Despite using first-order differencing, the implementation is able to produce visually realistic results by diverting fluid compression into eddying motions.