Measurements are presented of a resonant acoustic phenomenon occurring in a low-speed multi-stage compressor. The results show that this phenomenon shares many characteristics with acoustic resonance as measured in high-speed compressors. These similarities include a rotating pressure field, several acoustics frequencies corresponding to different circumferential modes, step changes in frequency as the flow rate is increased, and acoustic frequencies which are independent of flow coefficient, shaft speed and the axial length of the compression system. The paper includes measurements of the helical structure of the rotating pressure field and of the variation in amplitude of the acoustic signal over a stator exit plane.

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