Theoretical Study of Inlet-Distortion-Induced Instability of Axial Compression Systems

Abstract

A theoretical study is performed to investigate the stall triggering mechanism of inlet-distortion-induced instability of axial compression systems. The focus is on the transient stall inception processes when the compressor is throttled from stable operating conditions to stall. By including a model for steady circumferential distortion screens, a new system model captures the non-linear interaction between inlet distortion and the axial compressor. The model is then studied with direct numerical simulation. It is found that the unstable long length-scale disturbances always grow out of the regions of the spoiled sectors of the distorted background flow, but under certain conditions they may evolve into short length-scale disturbances before rapidly triggering the full size stall. This is due to the influence of the non-linearity of the compressor characteristic and the distortion screen characteristic. The phenomenon of the long-to-short disturbance evolution shows the interplay of the initiation of the stall precursors, which is heavily related to blade passage flows, and their evolution process, which is dominated by system's non-linear characteristics, and offers an explanation to similar experimental phenomenon observed by other researchers.