Internal Structure of Inertial Granular Flows

We analyze inertial granular flows and show that, for all values of the inertial number I, the effective friction coefficient mu arises from three different parameters pertaining to the contact network and force transmission: (1) contact anisotropy, (2) force chain anisotropy, and (3) friction mobilization. Our extensive 3D numerical simulations reveal that mu increases with I mainly due to an increasing contact anisotropy and partially by friction mobilization whereas the anisotropy of force chains declines as a result of the destabilizing effect of particle inertia. The contact network undergoes topological transitions, and beyond I similar or equal to 0.1 the force chains break into clusters immersed in a background soup of floating particles. We show that this transition coincides with the divergence of the size of fluidized zones characterized from the local environments of floating particles and a slower increase of mu with I.