A new model for the prediction of turbofan noise with the effect of locally and non-locally reacting liners

This paper presents a unified model to study the effect of both locally and non-locally reacting liners on the sound radiation generated by fan blade rotating sources. This model is set up by the following steps. First, the spinning mode eigenfunction expansions are used to obtain the solution of sound field inside the duct, while the effect of duct liner is modeled by distributed monopole sources, thus effectively avoiding the solution of a difficult complex eigenvalue problem. Secondly, in order to avoid the estimation of the generalized impedances at the inlet and exhaust planes, a boundary element method is used to give the solution outside the duct. With the suitable boundary conditions imposed on the inlet and exhaust planes, a matrix equation is obtained, and the relevant numerical calculation shows this model can not only give a good agreement with existing results for locally reacting liner but also has a capability to predict the sound radiation from fan rotating blade sources with an arbitrary combination of locally and non-locally reacting liners.