Characterization of clusters in rapid granular flows.
The clustering phenomenon within two-dimensional, rapid granular, simple shear flows is investigated. Two characterizations are developed and implemented for monodisperse systems, revealing physically meaningful insight. First, a new feature of the radial distribution function is identified for these dissipative granular systems, which is not present in molecular (nondissipative) systems. Namely, a long-scale minimum occurs at a distance representing the average distance between the center of a cluster and the center of a dilute region. Results indicate that center-to-center distances are least (i.e., clusters are most tightly packed) for systems of moderate particle concentrations and low restitution coefficients. In addition, concentration and temperature measurements of clustered and dilute regions are also obtained using a Gaussian filter that is based on this center-to-center distance and, thus, provides a means of appropriately defining local concentrations. These results confirm previous findings that cluster prevalence increases with decreasing dissipation and that clustered regions have lower temperatures than their dilute counterparts. Surprisingly, however, the results indicate that cluster prevalence, defined by normalized concentration differences between the two regions, decrease monotonically with an increase in overall particle concentration.