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Turbo-fan engines seek to achieve the highest compression ratios possible with the minimum number of parts by driving compressor stages to the extremes of their operating limits, which can risk compressor stall. This study expands on previous work by combining experimental and computational methods to evaluate the effectiveness of advanced transonic compressor casing treatments at increasing stall margin while minimizing losses. The NPS Turbopropulsion Lab Transonic Compressor Rig was used to characterize the performance of an advanced transonic compressor in the stage and stage-and-a-half configurations; additionally, inlet guide vanes were installed and evaluated. After characterization of the base performance, s-shaped axial endwall grooves were added to improve stall margin of the compressor stage. Experimental results proved the casing treatments were successful only in the subsonic regime. Stall margin increases of at least 286% were seen in low speed tests with 117% observed in high speed operation. Computational analysis simulated advanced casing treatments and effects of inlet whirl and was correlated to experimental data to shed light on the recirculation mechanisms active in casing treatments. The simulations provided insight for further development of novel self-recirculating endwall treatments and associated technologies., Office of Naval Research, Arlington, VA, 22217, Outstanding Thesis, Ensign, United States Navy, Approved for public release. Distribution is unlimited.

Compact self-recirculating injection that bleeds air from the casing downstream of a rotor blade row and injects the air as a wall jet upstream of the same rotor blade row is experimentally studied after the elaborated design of its structure. The bleed ports, injection ports, and recirculating channels are circumferentially discrete and occupy only 38% of the circumference. Separate tip air injection and outlet bleed air are simultaneously selected for comparison with the self-recirculating injection. Results show that the compact self-recirculating injection can improve the most stall margin by 6.12% among all the three cases on the premise of no efficiency penalty and can also enhance the efficiency (maximum of 1%) for only 0.47% of the total injected momentum ratio recirculated near stall. The details of the flow field are obtained using a multihole probe, a time-resolved Kiel probe, and pressure transducers. The detailed comparative analysis of the characteristic flow in terms of tip leakage flow, blade load, rotor wake feature, and blockage indicates that the self-recirculating injection can postpone the occurrence of stalling in the proposed compressor through a coupling influencing mechanism. One mechanism is to weaken the self-induced unsteadiness of tip leakage flow and to delay the forward movement of the interface between the tip leakage flow and the main flow. The other mechanism is to unload the blade tip and to recover the rotor wake. All these responses can lead to improved stall margin in the self-recirculating injection. This study may be helpful to guide the design of self-recirculating injection in actual application. © Institution of Mechanical Engineers.

As part of the Augmented Damping of Low Aspect Ratio Fans (ADLARF) program at the Compressor Research Facility (CRF), the Recirculating Cavity Casing Treatment was in test operation. The casing treatment was made of 6061-T6 aluminum alloy and was specially instrumented for the exploration of stall margin, performance data, and thermal effects. In addition to obtaining stall margin data, this casing treatment was part of a detailed test program to study the effects of five different casing treatments. After thermal cycling the casing treatment between ambient temperature and 650 deg F, the casing treatment failed after seven hours of test time. The casing treatment was removed and a failure analysis was performed. This paper will summarize the study findings and conclude with recommended actions.