  We numerically analyze the steady flow of two-dimensional granular materials
in a rotating drum using the discrete element method and a continuum model. The
velocity fields obtained from both methods are quantitatively consistent. Two
distinct regions exist in the granular flow: the surface flow layer and the
static flow regime associated with the rigid rotation near the bottom. The
thickness of the surface flow layer increases with the drum diameter and shows
a slight dependence on the angular velocity of the rotating drum. Scaling laws
for the velocity profile and the surface layer thickness are derived
analytically based on the continuum model. The validity of the scaling laws is
confirmed numerically.
