Unsteady interactions in supersonic compressor stages

The unsteady phenomena in the case of supersonic compressor flow are discussed on the basis of characteristic experimental results. The following conclusions can be drawn: the unsteady upstream disturbances caused by a supersonic rotor decrease hyperbolically and can be predicted by theoretic approaches for the relative flow; speeds generating slight supersonic relative inlet flow are critical for upstream interference; the downstream interference is caused by wakes and shockwaves; the unsteady pulsations in the stator increase with higher speeds; at high speeds the change of the flow angle is responsible for the unsteady effects; at lower speeds the influence of the velocity decay becomes more and more important; the unsteady fluctuations do not decrease continuously, but are intensified whenever shock oscillations are caused; and, finally, unsteady pulsations are able to influence the stage-performance particularly near the blockage-line.