Hydrodynamics of granular gases of inelastic and rough hard disks or spheres. I. Transport coefficients.

Abstract

The transport coefficients for dilute granular gases of inelastic and rough hard disks or spheres with constant coefficients of normal (α) and tangential (β) restitution are obtained in a unified framework as functions of the number of translational (d_{t}) and rotational (d_{r}) degrees of freedom. The derivation is carried out by means of the Chapman-Enskog method with a Sonine-like approximation in which, in contrast to previous approaches, the reference distribution function for angular velocities does not need to be specified. The well-known case of purely smooth d-dimensional particles is recovered by setting d_{t}=d and formally taking the limit d_{r}→0. In addition, previous results [G. M. Kremer, A. Santos, and V. Garzó, Phys. Rev. E 90, 022205 (2014)10.1103/PhysRevE.90.022205] for hard spheres are reobtained by taking d_{t}=d_{r}=3, while novel results for hard-disk gases are derived with the choice d_{t}=2,d_{r}=1. The singular quasismooth limit (β→-1) and the conservative Pidduck's gas (α=β=1) are also obtained and discussed.