Studies of granular surface flow in a rotating drum are of importance in both scientific and industrial field. However, little work has been found for high rotational speed drum in the literature, which has a wide uses, such as pharmaceutical, food, chemical and ceramic industries. In this paper, the granular flow in cascading regime is studied via particle image velocimetry (PIV) system in a quasi-two-dimensional rotating drum.

At high rotational speeds, the free surface profile no longer stays flat, and becomes increasingly S shaped with increase of Froude number (Fr=ω²R/g, where ω is the angular speed, R is the drum radius, and g the gravity acceleration). Particles can be divided into three regions, active, passive and particle raining regions. The influences of operational variables such as rotating speed and size ratio are discussed. Finally, simple equations are derived to describe the granular dynamics using the thin layer approximation theory.