Abstract
Acoustical lining in aircraft engine nacelles is an effective method for reducing fan/compressor noise. Combined with duct acoustics, prediction of the noise reduction performance for a perforated non-locally reacting liner is conducted in this paper, and the sound reflection and radiation of a lined finite-length duct is studied. On the basis of mode analysis method, a model for sound propagation in an infinite-length lined duct is developed in this paper. Combined with the sound fields in the duct and liner, the eigenequation is obtained and numerically solved. The preliminary results showed that the noise reduction performance of non-locally reacting liners is superior to that of locally reacting liners in the low frequency band. By adjusting the bias flow velocity and cavity depth, the active control of the noise reduction performance can be achieved. A modified Boundary Element Method (BEM) used in this paper to solve the acoustic radiation of axisymmetric bodies is able to eliminate the nonuniqueness problem and is computational efficient. With boundary element method and mode matching method, a model for sound propagation and radiation of a finite-length duct is developed. However, the numerical procedure still needs to be improved. The theoretical analysis and numerical results of a finite-length duct lined with the non-locally reacting liner in this paper may be valuable for further developing and improving the nacelle acoustic design system.