FEM/BEM combined model for prediction of sound propagation and radiation of a duct inlet

A finite element/boundary element combined method has been developed for the duct acoustic problem, using finite element method (FEM) to solve the acoustic transmission of inner acoustic field inside the duct, while employing boundary element method (BEM) to construct the artificial boundary condition for the far field radiation computation. The FEM and BEM were matched by the impedance continuity condition at the interface between the computational domains, and the combined numerical code was solved by a fast iteration algorithm. The validation of the model was first carried out by comparing the present results with the Levine-Schwinger solution for the sound radiation of a cylindrical pipe opening. Furthermore, the present model was used to simulate the sound propagation and radiation phenomenon for a simplified duct configuration of an aero-engine nacelle without flow. Finally, an analysis of the acoustic liner effect on the far field sound radiation was conducted based on the simulation results.