Boundary interactions for two-dimensional granular flows. Part 2. Roughened boundaries

The global behaviour of a granular flow is critically dependent on its interaction with whatever solid boundaries with which it comes into contact, whether they be used to drive, retard or simply bound the flow field. This paper describes the results of a computer simulation study of the effects of roughening boundaries by ‘gluing’ particles to the surfaces. Roughness is commonly used in experimental devices as a way of approximating a no-slip condition between a granular material and the driving surfaces. On a microscopic level, this produces a boundary that extends out into the flow field to the limit of the roughness elements. This has a strong effect on the way that forces, and, in particular, torque, is transmitted to the particles in the neighbourhood of the boundary.