Velocity profiles of granular flows down an inclined channel.

Highlights • Granular flows over a static pile have been investigated in an inclined channel. • The velocity profiles of the avalanches follow a pure parabolic decrease. • The velocity profiles can be predicted with the flow rate. • A shear-thinning viscosity model accounting for the velocity profile is deduced. Abstract Granular flows over a static pile have been investigated in an inclined channel. Instead of dividing the granular motions into fast flow with linear velocity profile and creeping motion with exponential velocity profile, we set the boundary of the flowing layer as the locus of points where the particle velocity decreases down to 1% of the surface velocity, and unify the granular motions with a single velocity profile making the application more convenient. The velocity profile of the granular flows follows a parabolic form, and can be predicted once the surface velocity or the flow rate is determined. Moreover, we propose a viscosity model to account for the parabolic velocity profile in the flowing layer, and validate this model by employing FT4 Powder Rheometer. The apparent viscosity is approximated as the sum of frictional and collisional-translational contributions. In analogy with the turbulent mixing-length theory, the momentum transfer is enhanced by the fluctuation, and the apparent viscosity in the granular flows depends both on the flowing-layer thickness and the local shear rate. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]