Friction in granular flows : a numerical implementation

The accurate phenomenological description of granular flows is a complex matter, because of the divided nature of the media and its remarkable properties, at the boundary between fluids and solids. The most convenient way to have an insight on the physics of the grains is to use a numerical model. This is done by considering each grain individually in a Lagrangian approach, solving the contacts with implicit contact laws that are suitable for shocks. The obtained model is validated for simple cases, and confronted to numerical and experimental results from the literature for the static and dynamic angles of repose. The model shows good agreement and is able to reproduce reported behaviours for the angles of repose, although only a qualitative check was made for the dynamic case. The model is used to simulate the mixing of particles in a rotating mill, and it was found that higher coefficient of friction and rotational speed increase the mixing speed, in a sufficient way to prevent segregation.