Swirling mean flow effects on locally reacting interstage liner

Abstract

Sound transmission through a finite-lined section in a rigid annular duct with swirling and sheared mean flow is analyzed with a new mode-matching method based on the conservation of the total enthalpy and the mass flow, which does not reduce to the conservation of the pressure and the axial velocity when the swirl is non-zero. It relies on a new projection method based on the property of the Chebyshev polynomials and on the scattering matrix formalism to yield transmission losses. This new method is first validated against a finite elements method tool in the uniform axial flow case, and then provides a parametric study of the effect of swirl. At low azimuthal mode order $m$ , the swirl amplifies the attenuation of the contra-rotating modes and makes the attenuation of the co-rotating modes decrease with a trend of a general shift of the transmission loss curve toward contra-rotating modes. A small rotation of the transmission loss curves at low $\left|m\right|$ is also generally observed. The boundary condition in the lined section has a small effect on the transmission loss, except close to the cut-on thresholds. Finally, the duct boundary-layer thickness has a significant effect on the cut-on modes and the transmission loss but not its profile.