Acoustic waves in a cylindrical duct with periodically varying cross section

Artikel i vetenskaplig tidskrift, 1983

The null field approach is used to study the propagation of acoustic waves in a rotationally hard-walled duct with periodically varying cross section. For a radius that varies sinusoidally along the axial distance, numerical computations give the axial wave number and the passbands and stopbands of the modes of the duct. In particular, small passbands are seen to exist even for very large variations in radius, and probably all the way to the point where the duct is cut off. We also present some plots which show the pressure pattern inside the duct.