Modelling of ducted noise sources in the proximity of acoustic liners

Abstract

This paper focuses on modelling and predicting the acoustic field generated by ducted point sources in close proximity to an acoustic liner. Two analytical models are presented. The first model comprises a point monopole or dipole source in an infinite lined duct based on an existing Green’s function. The predictions are compared with classic solutions for a source over an infinite lined plane and with a high frequency asymptotic duct approximation. The second model extends the Green’s function to include a liner section of finite length connected to hard-wall extensions by using mode-matching techniques. The new model features the inclusion of point sources in the vicinity of an impedance discontinuity. The accuracy of this model is demonstrated by comparison with reference FE solutions. Both models indicate a significant impact of the source proximity to the liner surface in the source power output. These models offer insight on the source modification effects beyond the conventional approach in the design of liners solely based on acoustic absorption.