A study of stall inceptions in a low-speed axial-flow compressor with various radial loadings

In this paper, the stall inceptions in a single-stage axial flow compressor with different high loading positions generated by various radial distortions are experimentally and numerically investigated. The results indicate that the stall limit varies with the radial position of the distortion significantly. The closer the position of distortion to the blade tip, the more unstable the compressor becomes. In addition, the results demonstrate that stall inception varies with radial distortion accordingly. While with the hub distortion, the compressor exhibits modal-like disturbances prior to the stall onset, the stall is triggered by the spike-like disturbances directly with the center and tip distortions. The flow mechanism is then further explored with numerical simulations. It is shown that in the hub distortion case, the separation region caused by local high loading in large flow rate can migrate to the tip region along the span as the compressor is throttled to the stall limit. This spanwise migration plays an important role in the formation of the modal-like disturbances. Compared to the hub distortion, the modal-like disturbance in the uniform inlet flow appears in a shorter period of time because it takes less time to initiate stall cell when the separation occurs. In the tip distortion case, the separation at tip dominates so strongly that no modal-like disturbances are found before the stall onset. A discussion is given at the end of this paper to explain why in some compressors, a modal inception emerges first and the stall is triggered by the spike later.