Here you can find some notes describing the hydrodynamic modes of the Navier-Stokes equation for the Inelastic Hard Spheres fluids.
They are referenced in the papers:
Extension of Haff's cooling law in granular flows, EuroPhys Letters
Noise Reduction and Pattern Formation in Granular Flows, International Journal of Modern Physics C.
October 1st, 1998, email@example.com