Kinematics of mono- and bidisperse granular flow in quasi-two-dimensional bounded heaps

Quasi-two-dimensional (2D) bounded heap flow is a useful model for granular flows in many industrial processes and natural phenomena. It belongs to the family of free surface flows inclined chute flow, rotating tumbler flow, and unbounded heap flow but is different from all of them in that the uniform deposition of particles onto the static bed results in the uniform rise of the heap and presumably simpler kinematics. The kinematics, however, is only imperfectly understood. We performed discrete element method (DEM) simulations to study monoand bidisperse granular flows in quasi-2D bounded heaps. The experimentally validated computational results show a universal functional form for the streamwise velocity profile for both monoand bidisperse systems when velocities and coordinates are scaled by the local surface velocity and the local flowing layer thickness. This holds true regardless of streamwise location, feed rate, particle size distribution and, most surprisingly, for bidisperse flows, the local particle concentration. We find that the local surface velocity decreases linearly in the streamwise direction, while the flowing layer thickness remains nearly constant with both quantities depending only on local flow rate and local mean particle diameter. We show also that the velocity profile normal to the overall flow, which is important in understanding segregation, can be predicted analytically from the streamwise velocity and matches the simulation results well.