THE UNSTABLE BEHAVIOR OF LOW AND HIGH-SPEED COMPRESSORS

By far the greater part of our understanding about stall and surge in axial compressors comes from work on low-speed laboratory machines. As a general rule, these machines do not model the compressibility effec ts present in high-speed compressors and therefore doubt has always ex isted about the application of low-speed results to high-speed machine s. In recent years interest in active control has led to a number of s tudies of compressor stability in engine-type compressors. The instrum entation used in these experiments has been sufficiently detailed that , for the first time, adequate data are available to make direct compa risons between high-speed and low-speed compressors. This paper presen ts new data from an eight-stage fixed geometry engine compressor and c ompares them with low-speed laboratory data. The results show remarkab le similarities in both the stalling and surging behavior of the two m achines, particularly when the engine compressor is run at intermediat e speeds. The engine results also show that, as in the laboratory test s, surge is precipitated by the onset of rotating stall. This is true even at very high speeds where it had previously been thought that sur ge might be the result of a blast wave moving through the compressor. This paper therefore contains new information about high-speed compres sors and confirms that low-speed testing is an effective means of obta ining insight into the behavior of high-speed machines.