Origin of self-induced unsteadiness in axial compressors

Abstract

This study investigated the instability mechanisms within the blade-tip region of a transonic compressor. The variations in these mechanisms were explored under different operating conditions using methods such as spectral analysis and vortex identification. The results and analysis enhance the comprehension of self-excited unsteadiness in axial compressors, identifying its initiation characteristics and prevalence under different operational conditions. The regular occurrence of self-excited pulsations in transonic rotors was confirmed, especially when the flow rates fall blow specific levels, causing spontaneous pulsations within the tip region that are notably different from the blade-passing frequency. The findings highlight the crucial influence of interactions between separation flow, leakage flow, and shock waves in generating these pulsations. The effects of clearance size on flow structure intensity were also categorized, revealing three distinct self-excited unsteadiness mechanisms. These range from pulsations caused by shock–boundary-layer separation at small clearance sizes to those induced by interactions between leakage flow and shock waves at larger clearances, and finally to pulsations initiated directly by the clearance vortices at significantly larger clearances. This detailed analysis provides valuable insights into the dynamics of self-excited unsteadiness, supporting the advancement of the design and performance optimization of compressors.