Abstract
Inception patterns of rotating stall in a low-speed axial-flow fan have been investigated by measurements of pressure and velocity fluctuations. Experiments have been carried out at two different stagger angle settings for rotor blades. At the design stagger angle, a short length-scale stall cell known as a "spike" and multiple short length-scale stall cells appear first. These stall cells then grow into a long length-scale stall cell as flow rate decrease. The spike and the multiple short length-scale stall cells induce a part-span stall, and the long length-scale stall cell induces a full-span stall. At the small stagger angle, a long length-scale disturbance known as a "modal" is observed first, and the modal and spikes then induces the long length-scale stall cell. It is concluded from these results that the rotating stall inception patterns depend on the rotor stagger angle.
