STALL INCEPTION MEASUREMENTS IN A HIGH-SPEED MULTISTAGE COMPRESSOR

This paper presents unsteady measurements taken in a high-speed four-s tage aeroengine compressor prior to the onset of aerodynamic flow inst abilities. In this experiment, 40 fast-response pressure transducers h ave been located at various axial and circumferential positions throug hout the machine in order to give a very detailed picture of stall inc eption. At all the compressor speeds investigated, the stall pattern o bserved is initiated by a very short length-scale finite-amplitude dis turbance, which propagates at a fast rate around the annulus. This ini tial stall cell leads to a large-amplitude system instability in less than five rotor revolutions. Varying the IGV setting angle is found to have a strong influence on the axial location of the first disturbanc e detected. In particular, transferring the aerodynamic loading from f ront to downstream stages moves the first disturbance detected from th e first to the last stage of the compressor. Other repeatable features of the stall inception pattern in this compressor have been identifie d using a simple analysis technique particularly appropriate to the st udy of short length-scale disturbances. It is found that the origins o f instabilities are tied to particular tangential positions in both th e stationary and rotating frames of reference. These measurements lead to the conclusion that the stall inception process in high-speed mult istage compressors can be characterized by some very local and organiz ed flow phenomena. Moreover, there is no evidence of prestall waves in this compressor.