The fast scattering method was developed in this paper

which could be used for predicting the acoustic propagation problems in the varying cross-section ducts with the acoustic liners. The method can handle the complex section relatively easily by using the direct boundary element method. The noise reduction of a real fan with the duct liners was predicted. The influence of the liner impedance and the sound scattering from the moving body was investigated by comparing the results with those given in the literature. The results illustrate that the present method can be used for the design of the duct liner in the engineering.