Investigations on Stator Hub End Losses and its Control in an Axial Flow Compressor

In an axial flow compressor, the presence of separated flow near the hub-end of a stator would result in an overall loss in the performance. In the present paper, stator hub-stall is attempted to be eliminated for a high hub-tip ratio (0.8) axial flow compressor stage consisting of a highly loaded rotor and stator. Numerical and experimental studies on an untreated straight stator (straight-stacked, twisted) blade show a large vortex near its hub. The large vortex is attempted to be reduced by modifying the present blade by (i) providing an additional twist at the hub-end of the stator blade (ii) providing a hub-clearance (a cantilevered blade fixed from the casing). The straight (untreated) stator, hub-end-bend version and the hub-clearance version are studied for two different rotor-tip clearances. Detailed computational analysis of the variation of hub-clearance at a fixed rotor-tip clearance is also carried out. Throughout the study, experiments are carried out on the above discussed different stator (untreated & hub-treated) configurations, in combination with the same rotor, at a fixed rotor-tip clearance. The studies show that the flow conditions are improved near the hub of the highly loaded stator blade both by the hub-end-bend design and by the hub-clearance provided.