K-1110 A Numerical Simulation of Rotating Stall in Axial Flow Fans

Abstract

Unsteady numerical simulatons are conducted for flows in axial rotors in rotating stall regime. Although numerical viscosity is inevitably introduced to stabilize computation to this highly complicated flow, the obtained flow reasonably explains the observations in experiments. It is confirmed that in some rotor geometry characterized by solidity, aspect ratio of a blade, hub ratio, etc., rotating stall cells never appear but several stall areas of various scales scattered along the casing wall are found, even though head characteristics shows rotating stall regime. In another rotor used in the numerical imulation, stable stall cells appear as observed in the corresponding experiments. However, the nature of the stall such as whether it is of reprsenting light stall or of heavy stall is not identified. It turned out that the rotating stall cell is a strong vortex tube which is generated by a strong jet ejecting toward upstream through a couple of inter-blade flow passages.