Eigenvalue analysis for acoustic multi-ports

Abstract

Acoustic multi-ports are commonly used to describe the scattering (the transmission and reflection) and the source of aero-acoustic components in duct and pipe systems. The components are therefore modeled as “black-boxes,” assuming linear and time invariant systems. Using linear network theory, two components can be combined to a cascade for which the scattering and sources are predicted. This step, however, requires decoupled components; the flow disturbances downstream of an aero-acoustic source can be large and turbulences impinging on the downstream component may change its acoustic properties. In this presentation, we show how to use eigenvalue equations in order to investigate this so called “installation-effect” on both, the scattering and the source of induct components. The theoretical results are compared with measurements in order to conclude on the changing source and scattering mechanisms.