A theoretical approach to sound propagation and radiation for ducts with suppressors

The several phenomena involved in theoretical prediction of the farfield sound radiation attenuation from an acoustically lined duct have been studied. These include absorption by the suppressor, termination reflections, and farfield radiation. Extensive parametric studies have shown that the suppressor absorption performance can be correlated with mode cut‐off ratio or angle of propagation. The other phenomena can be shown explicitly to be dependent upon mode cut‐off ratio. A complete system can thus be generated which can be used to evaluate aircraft sound suppressors and which can be related to the sound source through the cut‐off ratio‐acoustic power distribution. Although the method is most fully developed for inlet suppressors, several aft radiated noise phenomena will also be discussed. This paper summarizes this simplified suppressor design and evaluation method. Comparisons of noise suppressor data from engine experiments are compared to the theoretical calculations for farfield sound attenuation...

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