Determination of the impedance for lined ducts with grazing flow

Abstract

Passive means of acoustically damping devices like perforates or - more generally - liners play an important role in industrial applications to protect the community e.g against power plant noise´. In aero-engines, Helmholtz resonator type liners serve as substantial noise abatement means in regions of cold flow. An important physical property to characterize lining devices is the impedance. Several impedance eduction methods exist in literature, most of which are mathematically complicated or need substantial computation time. This paper presents a new impedance eduction method, which is relatively simple to apply, robust, and cheap in terms of computational effort. The method is derived and validated with NASA benchmark data. Its accuracy and applicability is demonstrated and approved.