Boundary effects on the angle of repose in rotating cylinders

The angle of repose for the flow of granular materials in a half-filled rotating drum is studied by means of experiments and computer simulations. Particles of different material properties are used to investigate the effects of the end caps on the angle of repose. By fitting the numerical results to an exponentially decaying function, we are able to calculate the characteristic range zeta of the influence of the wall. We found that zeta scales with the drum radius but does not depend on either the density or the gravitational constant. For increasing particle diameter, finite size effects are visible.