Instability of dilute granular flows on rough slope

We numerically study the stability of granular flow on a rough slope in a collisional flow regime in two dimensions. We examine the density dependence of the flow behavior in a low-density region, and demonstrate that the particle collisions stabilize the flow above a certain density in the parameter region where a single particle shows an accelerated behavior. Within this parameter regime, however, uniform flow is only metastable and is shown to be unstable against clustering when the particle density is not sufficiently high.