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.