| description abstract | Abstract. In a highly loaded axial-flow compressor, the type of stall inception transitions from a modal wave to a spike under tip radial distortion, while it remains a modal wave under hub radial distortion. To better understand the underlying physical mechanisms, we conducted an experimental investigation using high-resolution pressure measurements in the rotor blade tip region. Under uniform inflow and hub distortion, blade loading is highest at the midchord region and gradually shifts toward the leading edge as throttling progresses. In this scenario, large-scale flow separation develops on the blade suction side, followed by the emergence of unsteady tip leakage vortex. The onset of modal wave stall inception is found to be associated with the interaction between flow separation and tip leakage vortex, ultimately leading to leading-edge vortex spillage and subsequent rotating stall. When the inflow is distorted in the tip region, blade loading increases significantly and becomes concentrated near the leading edge. Thus, the unsteadiness of the tip leakage vortex intensifies, triggering tip leakage vortex spillage and the onset of classic spike-type stall inception. Given the distinct flow characteristics under uniform and distorted inflow conditions, we analyzed stall warning signals using autocorrelation and fast wavelet methods. Our results show that the autocorrelation coefficient gradually decreases, while the wavelet coefficient increases, revealing that unsteadiness in the blade tip region—originating from flow separation or tip leakage vortex—intensifies as throttling continues. Our investigation enhances better understanding of two typical stall inception mechanisms and provides valuable insights into stall warning strategies, particularly for cases where stall inception transitions occur under inlet distortion. | |
