Influence of granular temperature and grain rotation on the wall friction coefficient in confined shear granular flows

¹ Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan
² MAST-GPEM, Univ Gustave Eiffel, IFSTTAR, 44344, Bouguenais, France
³ Center for Advanced Study in Theoretical Sciences (CASTS), National Taiwan University, Taipei, Taiwan

^* e-mail: f00522316@ntu.edu.tw
^** e-mail: riccardo.artoni@univ-eiffel.fr
^*** e-mail: fulingyang@ntu.edu.tw
^**** e-mail: patrick.richard@univ-eiffel.fr

Published online: 7 June 2021

Abstract

A depth-weakening wall friction coefficient, µ_w, has been reported from three-dimensional numerical simulations of steady and transient dense granular flows. To understand the degradation mechanisms, a scaling law for µ_w/ f and χ has been proposed where f is the intrinsic particle-wall friction and χ is the ratio of slip velocity to square root of granular temperature (Artoni & Richard, Phys. Rev. Lett., vol. 115 (15), 2015, 158001). Independently, a friction degradation model has been derived which describes a monotonically diminishing friction depends on a ratio of grain angular and slip velocities, Ω (Yang & Huang, Granular Matter, vol. 18 (4), 2016, 77). In search of experimental evidence for how these two parameters degrade the µ_w, an annular shear cell experiment was performed to estimate the bulk granular temperature, angular and slip velocities at sidewall through image-processing. Meanwhile, µ_w was measured by a force sensor to confirm the weakening towards the creep zone. The measured µ_w/ f − χ and µ_w/ f − Ω were both well-fitted to the corresponding models showing that both granular temperature and angular velocity are significant mechanisms to degrade the µ_w which broadens the research perspective on modeling the boundary condition of dense granular flows.