Ray-theory predictions of the noise radiated from aeroengine ducts

This paper describes two significant extensions to the ray-acoustics approach for predicting the radiation of noise from sources inside aeroengine ducts. It describes first how diffraction effects can be included in the ray-acoustics model, using a statistical assumption which does not require detailed information about the source. For this purpose the source is characterized by its farfield directivity with diffraction effects neglected. Although the approach is developed for two-dimensional ducts it is applicable to ducts of more general interest. The paper then describes how interference effects can be modelled for both correlated and uncorrelated sources, by assuming an effective source directivity and then neglecting the interference of different rays. These two extensions to the ray-acoustics approach result in a flexible technique for predicting the radiated sound which is general enough to deal with most ducts of interest.