Prediction of the Acoustical Performances of Muffling Pipe Systems by the Method of Characteristics

Abstract

A numerical model is presented for the calculation of sound attenuation of flow duct systems in the frequency domain. The method of characteristics is used to solve the non-linear hyperbolic problem of plane wave motion in ducts. The basic conservation equations are not linearized, to achieve a comparison between linear model and gas dynamic model predictions. Boundary conditions providing acoustic excitation of the duct system are explained, and details are given about the calculation of the transfer functions of muffling pipe systems, including some numerical algorithms to achieve satisfactory predictions by the method of characteristics. End corrections have been introduced to take account of phase shifts in the wave reflection at open terminations as well as at abrupt area changes. A comparison between experimental attenuation curves, measured in a semi-anechoic room, and calculated ones is displayed for some simple geometries, including Helmholtz resonators and expansion chambers, and shows a fairly good agreement.