Acoustic waves in a cylindrical duct with infinite, half-infinite, or finite wall corrugations

Abstract

Time-harmonic acoustic waves in a cylindrical hard-walled duct with infinite, half-infinite, or finite wall corrugations are considered. The modes in the infinite corrugated duct are determined with the null field approach. The sinusoidally corrugated duct is studied numerically and the behaviour of the longitudinal wavenumber is closely investigated in both passbands and stopbands. The transmission and reflection soefficients for a junction between a straight and a corrugated duct are calculated by mode-matching and more complicated cases, such as a straight duct with a finite number of corrugations, can then be treated by a building-block method. Numerical examples are given which show reflection coefficients for a junction between a straight and a corrugated duct and also for a straight duct with a finite number of corrugations.