The unsteady aerodynamic flow field of the downstream stator in an advanced design 1&1/2 stage axial-flow compressor is experimentally investigated at both subsonic and transonic compressor operating conditions. The stator response at the subsonic rotor speed is mainly due to changes in the airfoil circulation distribution resulting from the incidence fluctuations generated by the passing of the rotor wakes. This is not the case for the transonic rotor speed in which phenomena associated with the intra-stator transport of the chopped rotor wake segments through the vane passage dominate the stator unsteady aerodynamic response characteristics. Rotor-IGV and rotor-stator interactions also generate static pressure fluctuations that act as an additional unsteady aerodynamic forcing function to the downstream stator. The spatial periodicity of these acoustic interactions is over the entire annulus of the machine due the unequal number of blades and vanes in the compressor, with the amplitude of the acoustic excitation to the downstream stator varying from vane-to-vane around the compressor annulus.

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