Applying the Campbell [4] criterion (for excitation of axisymmetric physical systems in proximity to turbomachinery) to an analytic model of an annular acoustic cavity, a detailed view of acoustic resonances in the cavity is derived. The perspective expands on the prior work of Tyler and Sofrin [1] and others by considering the entire spectrum of modes, and the effects of axial Mach number and swirl velocity in the inlet cavity, as well as the geometric proportions of the cavity. Noise data from an experimental turbomachinery vehicle are examined over a spectrum of rotative speeds by means of a narrow band filter tracking integer multiples of rotative speed. Many aspects of the predicted acoustic resonances at supersonic wheel speeds are substantially confirmed. Additionally, unexpected subsonic resonant peaks are observed and partially explained. Conclusions are drawn as to probable influence of the aerodynamic and geometric parameters in manipulating acoustic resonances out of the operating range of aircraft engines.

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