Discrete-frequency tones generated by rotor-stator interactions are of particular concern in compressor design. In the annular inlet and exit ducts, the acoustic waves are generated at the multiples of rotor blade pass frequency. Classical theory considers an isolated flat-plate cascade of identical uniformly spaced airfoils. The current analysis extends this tuned isolated cascade theory to consider coupled aerodynamically detuned cascades where aerodynamic detuning is accomplished by changing the chord of alternate rotor blades and stator vanes. In a coupled cascade analysis, the configuration of the rotor influences the downstream acoustic response of the stator, and the stator configuration influences the upstream acoustic of the rotor. This coupled detuned cascade unsteady aerodynamic model is first applied to a baseline stage configuration. This baseline stage is then aerodynamically detuned. The nominal aerodynamically detuned stage configuration is then optimized, with the stage acoustic response decreased 5dB upstream and 6 dB downstream at the design operating condition.
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