Dynamics of Freely Cooling Granular Gases

X. Nie, E. Ben-Naim, and S.Y. Chen

We study dynamics of freely cooling granular gases in two-dimensions using large-scale molecular dynamics simulations. We find that for dilute systems the typical kinetic energy decays algebraically with time, $E(t)\sim t^{-1}$, in the long time limit. Asymptotically, velocity statistics are characterized by a universal Gaussian distribution, in contrast with the exponential high-energy tails characterizing the early homogeneous regime. We show that in the late clustering regime particles move coherently as typical local velocity fluctuations, $\Delta v$, are small compared with the typical velocity, \hbox{$\Delta v/v\sim t^{-1/4}$}. Furthermore, locally averaged shear modes dominate over acoustic modes. The small thermal velocity fluctuations suggest that the system can be heuristically described by Burgers-like equations.

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