Determining the pressure modes at high frequencies in lined ducts with a shear flow

Noise transmission problems where sound propagates in flow ducts occur in a variety of contexts. The work in this paper is motivated by the turbofan aircraft engine application. Simulating the acoustics of turbofan duct systems is a challenging problem because this can necessitate the modelling of high-frequency sound propagation in ducts containing sheared mean flow and with acoustically-lined walls. The purpose of this work is to develop fast and efficient simulation methods, that can be used to calculate the propagation of sound in lined flow ducts. In this paper, preliminary results are presented obtained from a new finite element code which has been developed specifically to determine the pressure modes in ducts containing shear flow. The formulation of the finite element method is outlined. Preliminary results are shown which compare the duct modes with different boundary layer profiles. These results provide examples of finite element solutions of pressure modes in an annular duct. The results show how the shape of the boundary-layer profile can affect the duct modes