Unsteady Upstream Effects in Axial-Flow Supersonic Compressor Stages

An investigation of the unsteady flow effects in a supersonic compressor stage is reported. Semiconductor transducers mounted in the casing, a stroboscopic schlieren-technique and probes equipped with semiconductor transducers were used to obtain unsteady static pressure, flow visualization and three-dimensional flow information, respectively. The throttling effect during the starting procedure of the stage was found to produce changes of the quasi-steady and unsteady rotor flow pattern as well as changes in both amplitude and frequency of the flow disturbances at the inlet. The conditions which are generated in this way at design speed are different from those reached by back-pressure imposed on the started supersonic rotor at the same speed. The relative position of rotor and stator has an influence on the flow field only below design speed. One can conclude from the measurements of the rotor outlet angle that these effects generated by throttling the rotor flow by a stator during the starting procedure might be avoided with movable stator blades.