A time-domain method for duct acoustics

This paper reports the development of a time-accurate method for prediction of acoustics in lined ducts. The multi-dimensional Euler equations are dimensionally split into a system of uni-directional simple wave equations, which are discretized and solved using an implicit compact high order finite-difference scheme. The split equations are closed and coupled through the concept of impedance at domain boundaries. Time-domain extensions of the impedance boundary condition and their efficient implementation are introduced for broadband and monotone waves. The method is benchmarked by the modal solution of a monopole in the lined duct, and used to investigate wall interference on the acoustic fields of realistic sources. Excellent agreement is found in the comparison with classical solutions, and the discrepancy found in the comparison with experiment is ascribable to experimental uncertainty. (C) 2000 Academic Press.