Fast decay of the velocity autocorrelation function in dense shear flow of inelastic hard spheresAshish V. Orpe1, V. Kumaran2, K. Anki Reddy2 and Arshad Kudrolli1
1 Department of Physics, Clark University - Worcester, MA 01610, USA
2 Department of Chemical Engineering, Indian Institute of Science - Bangalore 560012 India
received 26 September 2008; accepted in final form 18 November 2008; published December 2008
published online 12 January 2009
We find in complementary experiments and event-driven simulations of sheared inelastic hard spheres that the velocity autocorrelation function decays much faster than t-3/2 obtained for a fluid of elastic spheres at equilibrium. Particle displacements are measured in experiments inside a gravity-driven flow sheared by a rough wall. The average packing fraction obtained in the experiments is 0.59, and the packing fraction in the simulations is varied between 0.5 and 0.59. The motion is observed to be diffusive over long times except in experiments where there is layering of particles parallel to boundaries, and diffusion is inhibited between layers. Regardless, a rapid decay of is observed, indicating that this is a feature of the sheared dissipative fluid, and is independent of the details of the relative particle arrangements. An important implication of our study is that the non-analytic contribution to the shear stress may not be present in a sheared inelastic fluid, leading to a wider range of applicability of kinetic theory approaches to dense granular matter.
47.57.Gc - Granular flow.
45.70.Mg - Granular flow: mixing, segregation and stratification.
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