Effects of end wall friction in rotating cylinder granular flow experiments

Dry granular flows in half-filled horizontal rotating cylinders were studied by NMR to ascertain end wall effects. We measured the velocity and density profiles in planes perpendicular to the axis of the drums for three cases: (1) Near the end wall of a long "3D'' cylinder, (2) Near the middle of the long cylinder and, (3) For the whole of a short "2D'' cylinder. The velocity near the free surface is fastest for the short cylinder and slowest near the end wall of the long cylinder. We believe that these differences are due to friction between the beads and the end walls, speeding up the flow for the 2D drum and reducing the near-wall speed for the 3D drum.