A computational mode-matching approach for sound propagation in three-dimensional ducts with flow

A finite element (FE) mode-matching approach is presented for duct acoustics with flow and circumferentially varying liners. The primary application of the method is the prediction of sound attenuation in turbofan inlets and bypass ducts including the effects of liner splices. A fully numerical procedure has been developed to determine the acoustic modes in ducts of arbitrary cross-section and mean flow profile. A numerical mode-matching method is proposed using a modified matching technique in order to deal more accurately with liner discontinuity with flow. An analytic radiation model can also be integrated with the mode-matching procedure in order to obtain far-field directivity for tones and broadband multimode noise. The accuracy of the mode-matching method is demonstrated by comparison with exact solutions and high-resolution FE solutions. The influence of non-axisymmetric liners on noise radiation is also illustrated.