Stability Enhancement Using Foam Metal Casing Treatment Subjected to Different Flow Uniformities

Abstract This study experimentally and numerically investigates the formation mechanisms of different stall inception of an axial fan under three radial loading configurations—uniform (UNI), tip distortion (high tip loading-HTL), and hub distortion (low tip loading-LTL)—and evaluates the stability enhancement effects of a casing treatment. A radial distortion generator is employed to change the radial distribution of rotor loading, enabling the switch of stall inception type. Results indicate that HTL induces low axial velocity and high tip loading at the blade tip region, while LTL produces the opposite trend. With UNI and HTL, the fan stalls via the spike-type stall inception. While in the case of the LTL, the fan experiences a long-length-scale disturbance stall inception, and a large flow separation appears on the suction surface of the rotor blade near the stall point. It is further found that extending the stall margin improvement generated by the casing treatment does not always depend on the type of stall inception. The possible stall margin improvement mechanisms of the casing treatments are also discussed.