An extensive duct acoustics propagation study is presented that has been conducted to assess the design of a liner for an aeroengine inlet duct. The aim is to predict how different liner configuarations, at various flight conditions affect the attenuation of sound in an inlet. Two different noise source models are used: single mode and multimode. These represent the two principal fan noise sources: tonal and broadband noise. The two noise source models are then combined to predict the overall attenuation. An optimization procedure based on a response surface model is presented, to investigate a uniform and an axially segmented acoustic liner. The objective function used in the optimization is based on an approximate calculation of the perceived noise level. The aim is to utilize and axially segmented liner to increase, compared to a unifrom liner, the overall sound attenuation that is predicted. The main feature that emerges is that it is possible to increase the attenuation with an axially segmented liner only when a limited number of propagating modes are present.
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