A STUDY OF SPIKE AND MODAL STALL PHENOMENA IN A LOW-SPEED AXIAL COMPRESSOR

This paper presents a study of stall inception mechanisms in a low-spe ed axial compressor. Previous work has identified two common flow brea kdown sequences, the first associated with a short length-scale distur bance known as a ''spike,'' and the second with a longer length-scale disturbance known as a ''modal oscillation.'' In this paper the physic al differences between these two mechanisms are illustrated with detai led measurements. Experimental results are also presented that relate the occurrence of the two stalling mechanisms to the operating conditi ons of the compressor. It is shown that the stability criteria for the two disturbances are different: Long length-scale disturbances are re lated to a two-dimensional instability of the whole compression system , while short length scale disturbances indicate a three-dimensional b reakdown of the flow-field associated with high rotor incidence angles . Based on the experimental measurements, a simple model is proposed t hat explains the type of stall inception pattern observed in a particu lar compressor. Measurements from a single-stage low-speed compressor and from a multistage high-speed compressor are presented in support o f the model.