Computational study of erosion and deposition in transient granular flows on an erodible heap

We study, using Discrete Element Method (DEM) simulations, the transient response of an initially steady surface granular flow on a heap of the same material, when the heap is tilted by a small, positive or negative, angle. The system does not have sidewalls, unlike many previous studies. Upon application of the tilt, the height of the free surface, the height of the interface between the flowing and static zones, and the angle of the interface vary exponentially with time while approaching a steady state. A parametric study is conducted considering different mass flow rates, interparticle friction coefficients, particle diameters, and tilt angles. Local rates of erosion and deposition (Γ_{i},i=e,d), calculated at the interface, follow predictions of the models of Bouchaud et al. [J. de Phys. I 4, 1383 (1994)10.1051/jp1:1994195] and Boutreux et al. [Phys. Rev. E 58, 4692 (1998)1063-651X10.1103/PhysRevE.58.4692] with Γ_{i}=v_{i}(β-β_{n}) where v_{i} is the erosion velocity, β is the angle of the interface, and β_{n} is the neutral angle at which there is no erosion or deposition. The erosion velocity v_{e} is significantly larger than the deposition velocity v_{d} for all the cases studied, with v_{e}/v_{d}≈1.7. The erosion velocities are nearly independent of the mass flow rate in the layer, the interparticle friction, and the tilt angle. The velocities increase with particle diameter d and flowing layer thickness δ_{i} as v_{i}∼d^{1/2}δ_{i}.