Experimental characterization of the stable operating range of a highly-loaded low-pressure compressor stage

The current environmental legislation and the growth of the aviation sector observed in the last years is demanding the development of modern aircraft architectures to reduce CO2 and NOx emissions. Short-nacelle Geared High-ByPass turbofans and Boundary-Layer-Ingestion engines have shown strong potential to overcome this problem, despite they force the engine to operate under inlet non-uniform flow conditions. Overall, a renewed interest in the analysis of distorted machines is arising in recent years as traditional methods need to be modified for the design of distortion-tolerant engines. Despite extensive studies can be found on the front fan, the literature still lacks of information concerning the impact of real distortions on engine-representative compressors. In this context, the von Karman Institute for Fluid Dynamics is conducting leading research activities for the characterization of low-pressure compressors under distorted inflows. However, before going into the characterization of the machine under distorted conditions, it is necessary to establish a baseline understanding of the machine with a clean inlet flow, so that the impact of the distortion can be properly quantified and assessed. The objective of this Master’s Thesis is to conduct an extensive experimental campaign in the stable operating range of a high-speed low-pressure axial compressor. The main target of the present work is to provide an overview of the leading mechanisms for aerodynamic stall in clean conditions while identifying the critical flow features for stability. Initial assessments involve the determination of the stage overall performance across different corrected speeds and operating points of the machine through time-averaged measurements. Subsequently, span-wise distributions and maps of the flow field at the rotor and stator outlet are provided by means of pneumatic and fast-response instrumentation. From the results, it will be observed that the hub corner separation shows a critical increase close to the stability limit of the stage, due to the abrupt variation of the inlet incidence. Moreover, a tentative explanation about the development of a low total pressure region in the middle of the passage at the outlet of the stage is given. This activity is meant to provide an experimental dataset for the analysis and characterization of highly-loaded low-pressure compressors. The outcome of the present thesis is thought to provide an important contribution to the literature and to the design of modern axial compressors.