Acoustic wave propagation in a two‐dimensional flexural duct in the presence of a uniform flow

Abstract

An investigation was made of the phase velocity of acoustic waves propagating in a two‐dimensional flexural duct with a uniform flow. The flexural duct considered herein is composed of two parallel, thin elastic plates. The outer surfaces of the duct are in contact with a stationary fluid medium and its inside contains a uniform fluid flow. An eigenvalue problem was formulated for a two‐dimensional flexural duct by satisfying pertinent boundary conditions across the fluid‐plate interfaces. The acoustic pressure inside the duct is a summation of partial wave pressures, each of which is associated with a wave mode having its own phase velocity. Some of these waves are propagating in the duct without attenuation, whereas others are decaying as they travel along the duct, or are not capable of being propagated in the duct. It is found that the wave modes of which phase velocities are larger than the sound velocity of the outer stationary medium radiate sound energy outward.