Characterization of Transonic Fan Response to Inlet Distortion

Abstract

This thesis seeks to characterize transonic fan response to three-dimensional inlet flow distortion, which is a challenge of business jet propulsor-airframe integration. The specific context is ensuring fan operability in crosswind while retaining high cruise efficiency. A body force approach is used with a pre-processing workflow that simplifies the inputs of the body force model. This enables rapid assessment of changes to the fan work distribution, a step towards achieving potential benefits of fan-inlet co-optimization. The workflow is used to explore the sensitivities of fan response to an applied non-uniformity, to fan work distribution, and to bulk swirl. Incidence, as a metric for evaluating distortion, is found to offer an improved assessment of fan operability trends compared to metrics that only depend on the stagnation pressure distribution. Such metrics are not found to capture sensitivities of fan response to increasing circumferential extent of the stagnation pressure defect. Sensitivity of the local response of the fan in the low stagnation pressure region to the radial work distribution are dominated by effects seen in 2D distortions: steeper local pressure ratio characteristics increase the attenuation of the stagnation pressure non-uniformity. However, such designs generate more severe stagnation pressure non-uniformities downstream of the rotor at other spanwise positions due to radial variations in the distortion pattern and rotor pressure rise. The effect of bulk swirl on the characteristic slope produces coupling of stagnation pressure and swirl, where combined counter-swirl and stagnation pressure distortion is found to produce more severe fan operability penalties than the superposition of each separate effect. The characterization of inlet distortion response contributed by this thesis is a necessary step in optimizing the propulsor inlet design with constraints on off-design operability.