  We present a numerical simulation of a granular material using hydrodynamic
equations. We show that, in the absence of external forces, such a system
phase-separates into high density and low density regions. We show that this
separation is dependent on the inelasticity of collisions, and comment on the
mechanism for this clustering behavior. Our results are compatible with the
granular clustering seen in experiments and molecular dynamic simulations of
inelastic hard disks.
