Inclined granular flow in a narrow chute

In this paper we presents a detailed description of granular flow down a flat, narrow chute using discrete element method simulations, with emphasis on the influence of sidewalls on the flow. The overall phase diagram is provided and it is found that there are four flow regimes (no flow, bulk flow, surface flow, and gas flow). The H̃ stop curve is very complicated and quite different from that in the case without sidewalls. The effective friction coefficient $ \mu_{{\rm w}}$ increases with pile height H̃ and a surface flow occurs when the inclination angle $ \theta$ exceeds a critical value. The profile of $ \mu_{{\rm w}}$ shows that the $ \mu (I)$ rheology is valid in boundary layers. Furthermore, $ \mu_{{\rm w}}$ increases with the velocity of particles and there is a saturation to a nonzero value in static heap. For small H̃, the static heap vanishes and there is a bulk flow. A similarity between basal particles and sidewall particles indicates a universal role of the boundaries. In this bulk flow, there is a transition of the velocity profile with wall friction $ \mu_{{\rm ps}}$. When $ \mu_{{\rm ps}}$ is large, the velocity is linear and decreases with increasing height. With small $ \mu_{{\rm ps}}$, the velocity is nonlinear and the flow rate is roughly proportional to H̃ 3/2