An experimental investigation was carried out to examine the effects on stall margin of flow injection into, and flow removal out of, the endwall region of an axial compressor blade row. A primary objective of the investigation was to clarify the mechanism by which casing treatment (which involves both removal and injection) suppresses stall in turbomachines. To simulate the relative motion between blade and treatment, the injection and removal took place through a slotted hub rotating beneath a cantilevered stator row. Overall performance data and detailed (time-averaged) flowfield measurements were obtained. Flow injection and removal both increased the stalling pressure rise, but neither was as effective as the wall treatment. Removal of high-blockage flow is thus not the sole reason for the observed stall margin improvement in casing or hub treatment; injection can also contribute significantly to stall suppression. The results indicate that the increase in stall pressure rise achieved with injection is linked to the streamwise momentum of the injected flow, and it is suggested that this should be the focus of further studies.

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