A numerical simulation of rotating stall in axial flow fans

Unsteady numerical simulations 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. In a certain rotor geometry characterized by solidity, aspect ratio of a blade, hub ratio, etc., stable rotating stall cells appear, as observed in the corresponding experiments, but in another rotor, they do not. It turned out that the rotating stall cell is a unified strong vortex tube which emerges from a couple of inter-blade flow passages. The body of vortex has different moving velocity depending on its portion. Its uppermost part is a stable, nearly two-dimensional vortex and distortion of whole flow field having rotating stall cell is attributed to the flow induced by the vortex. The nature of the stall such as whether the obtained stall is representing light stall or heavy stall has not been identified.