Cooperative and uncooperative motions in gravity-driven flows

We present results from experiments and complementary molecular dynamics simulations of 2D gravity driven granular flows. We specifically study silo flow: discharge through an aperture in a rectangular cell. We obtain particle-scale data in our experiments using high-speed, high-resolution video. We find the presence of cooperatively moving regions and characterize them by their sizes, speeds, and lifetimes. We also find the presence of regions of high nonaffine motion and characterize them similarly. In our analysis, we place particular emphasis on the role of initial packing structure on the resulting bulk flow behavior and microscopic deformations. Our results suggest that the transition from clogging behavior to free flow can be modified by changing the packing structure.