Weakly frictional granular gases

Hydrodynamic equations of motion for a monodisperse collection of weakly frictional spheres have been derived from the corresponding Boltzmann equation, using a Chapman-Enskog expansion around the elastic smooth spheres limit. The hydrodynamic fields required in this case are: the velocity field, V(r,t), the translational granular temperature, T(r, t), and the (infinite) set of number densities, n(s, r, t), corresponding the continuum of values of the spin, s. An immediate consequence of these equations is that the asymptotic spin distribution in the hemogeneous cooling state for nearly smooth, nearly elastic spheres, is highly non-Maxwellian.