Precollisional velocity correlations in a hard-disk fluid with dissipativecollisions - art. no. 031306

Velocity correlations are studied in granular fluids, modeled by the inelas tic hard sphere gas. Making a density expansion of the Bogoliubov-Born-Gree n-Kirkwood-Yvon hierarchy for the evolution of the reduced distributions. w e predict the presence of precollisional velocity correlations. They are cr eated by the propagation through correlated sequences of collisions (ring e vents) of the velocity correlations generated after dissipative collisions. The correlations have their origin in the dissipative character of collisi ons, being always present in granular fluids. The correlations, that manife st microscopically as an alignment of the velocities of a colliding pair pr oduce modifications of collisional averages. in particular. the virial pres sure. The pressure shows a reduction with respect to the elastic case as a consequence of the velocity alignment. Good qualitative agreement is obtain ed for the comparison of the numerical evaluations of the obtained analytic al expressions and molecular dynamics results that showed evidence of preco llisional velocity correlations.