Impulse distributions in dense granular flows: Signatures of large-scale spatial structures

We study the impulse distribution in a model of gravity-driven granular flow and show that changes in the distribution are correlated with the appearance of clusters of "frequently-colliding" particles. Our simulations show increasingly large linear clusters as the flow velocity decreases. The dissipative nature of the collisions leads to an increase of small-impulse events as the size of these clusters grow and can explain the observed changes in the impulse distribution as the flow rate decreases.