Abstract The film flow characteristics on surface of rotary biological contactor (RBC) were numerically simulated using Computational Fluid Dynamics (CFD) method and the volume of fluid (VOF) model. The pattern of liquid film formation, film thickness and velocity distribution on the solid disc and window disc were investigated, respectively. The effects of the disc thickness on the pattern of liquid film formation and film thickness were also investigated. The results showed that the liquid film transited smoothly on the solid disc while the liquid film on the window disc dramatically changed in the location near the window area, and many irregular bubbles were found in the tank below the liquid. The film thickness decreased rapidly with the increase of the angle in the rising zone but kept unchanged in the dropping zone. The velocity of free film and its update frequency on the window disc were faster than those of wall-bound film. Within the scope of this research, the thickness of free film on the window disc increased with the increase of the thickness of disc.
