MNJSTRY OF AVlATfON

An experimental investigation of the effects of stage matching on compressor surge-by-This paper summarises some exploratory tests on o low speed low pressure ratio multi-stage a;:ial compressor, in rJhich mism2Ltchi.q w&s simulated by appropriate staggering of the stages, the last ztrgo alone being unchanged. Overall and stage characteristics anil surge flow coefficients were determined for two degrees of mismatching and for the fully matched condition. In addition, velocity and yaw traverses were made at the first and kst stages, and flow fluctuation measurements were also made at selected positions. In the two mismatched builds, the surge flow coei"ficients were found to be identical, and were higher than the value for the matched build. This corresponds with the phenomenon sometimes noted on high pressure ratio compressors, in which surge at speeds near the matched condition may tend to occur at a constant value of the flow coefficient at the last stage, and at lower speeds at a constant higher value, The tests appear to suggest thr,t the velocity profile at the last stage may be one sigtxificant 1: "ector in the determination of the surge point of a compressor. It is also suggested that flow visualisation technic~ues could provide useful detailed cLualitative information on the internal flow conditions of a compressor before and after the surge point, Previously issued as N.