ROTATING STALL AND SURGE IN AXIAL FLOW COMPRESSOR

Supported by the funds of the national natural science,we have tested and meassured the instability behavior of compressors in detail with hot-wire,hot-film probes and transient pressure 3-hole probes on single rotor,single stage and multi-stage compressors respectively.After analyzing signals with the power spectra and correlation analysis,it is found that there are two kinds of disturbances—peripheric oscillation and axial oscillation in the flow.On the basis of this fact,we propose the concept that the flow separation from airfoils results in peripheric oscillation and axial oscillation simultaneously,and provide a new model to describe the flow destabilizing mechanism. For the stability problem of multistage axial flow compressors,it is of practical value to investigate its stability limits,inclusive of the rotating stall margin.The preliminary results of this investigation show that the stability limit in the high speed regionis equivalent to a surge line,that the stability limit the middle speed region is indeed a stall line,and that the stability limit in the low speed region has two branches,one is the stall line of the whole compressor,the other is the rotating stall inception margin of the first stage.Both are of the same importance from the viewpoint of engine safety.Finally the mathematical methods for predicting the stability limits are discussed.