Unified scaling law for wall friction in laterally confined flows of shape anisotropic particles

In this work we discuss a scaling law for wall friction weakening in three-dimensional, dense, fully confined granular flows made of shape anisotropic particles. Using particle -based simulations, we observe a rich variety of kinematics and wall stress profiles by varying the particle-wall friction coefficient and the cell width. We show that in this peculiar flow configuration: (i) particle shape has a negligible influence on translational velocity and granular temperature profiles while the angular motion is strongly hampered for elongated particles and (ii) the mobilization of friction at the sidewalls is affected by both particle shape and flow pattern. Associating data on wall stress and particles kinematics, we find that wall friction mobilization is well described by a scaling law based on a balance between sliding and rolling motion of the grains. We show that the proposed scaling law seems to be very robust, being independent of the main system parameters, e.g., particle-particle friction, particle-wall friction, channel width, vertical confinement, particle elongation, and flow configuration (shear driven or gravity driven). This result highlights the importance of angular motion of the particles for the understanding of the behavior at flat boundaries and may reignite the debate about the relevant variables in theories for dense granular flows.

Automated summary

In this work, a scaling law for wall friction weakening in three-dimensional, dense, fully confined granular flows made of shape anisotropic particles is discussed through particle-based simulations. The study reveals that particle shape has limited influence on translational velocity and granular temperature profiles, but significantly affects angular motion. The mobilization of friction at the sidewalls is influenced by both particle shape and flow pattern. The proposed scaling law for wall friction mobilization, based on a balance between sliding and rolling motion, is found to be robust regardless of various system parameters.