Unstable mass flowrates in single stage axial compressors utilized by modern military aircraft can rapidly cause the compressor to stall, ultimately resulting in the potential loss of an aircraft or the lives of personnel. Although axial slot and circumferential groove casing treatments have been effective at increasing the margin to stall, they have traditionally been unsuccessful on the NPS military fan when operating in its highest speed configuration. Two different types of self-recirculating flow control casings were designed and tested in multiple flow configurations on the NPS transonic compressor rig and were able to improve the stall margin and enhance the stable operating mass flow range in all tested speed configurations. This dissertation reports the design, manufacture, and results obtained from the flow control casing experiments on the NPS transonic compressor rig. Utilizing computational fluid dynamics software, this dissertation also investigated the mechanism by which the NPS military fan stalled at both subsonic and transonic operating speeds, and the mechanism by which self-recirculating flow control extended stall margin where previous casing treatments have failed. Finally, proposed is a theory for why flow control designs that increase rotor tip loading through the addition of counter-swirl injection provide greater operational enhancement and stability over those that unload the rotor tip through the addition of co-swirl.

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Commander, United States Navy

ONR, Arlington, VA

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