Studying the weak effect of particle friction on the velocity profile of steady dry granular flows in a rotating drum

This work employs discrete element simulation to study why the velocity and kinetic energy of steady granular flows in a half-filled smooth frictional rotating drum show weak dependence on inter-particle friction in rolling regime. When the friction coefficient f is increased, noticeable rise of dynamic angle of repose beta and potential energy (PE) is observed with nearly merged velocity profile and slightly increasing kinetic energy. Particle interaction energy is analyzed revealing dissipation of the excessive PE by frictional slider and normal damper in the contact model. The latter consumption is analyzed since the normal force model is independent of f. A bulk with larger f avalanches at larger beta and particle random motions are higher (shown through granular temperature) permitting greater normal relative velocity u(N) but lower contact number N-c. Scaling analysis predicts the normal damping energy to change with u(N)(11/5) N-c and hence the faster growing uN counteracts the diminishing N-c when f is increased to dissipate more PE. Normal and tangential strain energy also stores more PE with f but at a much reduced magnitude as compared to the portion dissipated.