Effect of axially segmented liner distribution on sound attenuation in a flow duct

In turbofan aero-engines, the fan noise is normally defined as dominant tonal noise with harmonics and broadband random noise, and its control is challenging work.To achieve better attenuation of high order tones, an axially segmented liner can be used. This study modelled the sound propagation in a cylindrical duct with axially segmented by the modified mode-matching method. The liners are locally reactive, and numerical simulations verify the propagation model. The distribution of at most three liner sections is investigated and their attenuation effect is discussed. It is found that the total transmission loss is mainly determined by the surface area of different liners sections and the overall performance of the axially segmented liner can be approximately expressed as a linear combination of the performance of individual liners. Keywords: Acoustic liner, mode-matching method, transmission loss