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Numerical Investigation of the Influence of Axial Overlap of Blade Angle Slots on an Axial Flow Compressor Stability
Author(s): Haoguang Zhang, Wenhao Liu, Enhao Wang, W. L. Chu, Jingjing Yang, Weiguang Zhao
Keywords: Compressor, casing treatment, slots, stability, axial overlap
In this paper, a numerical investigation was conducted on a subsonic axial flow compressor rotor with blade angle slot casing treatments. The purpose of the investigation is to reveal the influence of axial overlap of blade angle slot on the compressor stability. Six kinds of blade angle slot casing treatments with different axial overlap rates(0.2, 0.3, 0.4, 0.6, 0.8 and 1.0), were designed in the numerical investigations. The unsteady calculated results show that with the increasing of axial overlap rates from 0.2 to 0.6, the stall margin improvement(SMI) generated by the slots becomes large little by little, and the slots with 0.6 axial overlap rate can generate 62.51% SMI. However, the slots with 0.2 axial overlap rate makes negative influence on the compressor stability with -5.28% SMI. When the axial overlap rates are increased to 0.8 and 1.0, the SMI values for the slots are reduced to 47.63% and 14.01% respectively. Besides, the slots with axial overlap rate of 0.4 cause the least penalty in peak efficiency among six kinds of slot casing treatment, and the peak efficiency for the slots with 0.4 axial overlap rate is 0.07% higher than that for smooth wall casing treatment. The slots with 1.0 axial overlap rate generate the biggest peak efficiency loss of 5.02% among six kinds of slot casing treatment. The flow field analyses show that the bleeding flows formed inside slots can remove the adverse tip leakage vortex, which is the critical factor making the onset of the rotor stall. With the increasing of axial overlap rate of the slots, the relative position between bleeding flows in the slots and tip leakage flow plays an important role in the stall margin improvement. Besides, the interaction between recirculated flows inside slots and main flows inevitably causes additional flow losses. With the increasing of axial overlap rate of the slots, the intensity and range of interaction between recirculated flows and main flows will become larger, and more flow losses will be caused.