Impedance eduction in the presence of shear flow

Abstract

This paper presents a method for educing acoustic liner impedance in the presence of grazing shear flow. The key features of the method are a numerical solution to the linearized frequency-domain equations of mass, momentum, and energy conservation, and the minimization of an objective function. As an application, the method is used in conjunction with measurements taken in the NASA Langley Flow Impedance Test Facility to educe the liner impedance of two dissimilar liners in the presence of a parallel, mean shear flow. Results show that the liner impedance educed in the presence of mean shear flow can differ significantly from that educed when only uniform flow is modeled. Thus, the importance of accurately modeling the effects of mean shear to educe liner impedance is demonstrated. Nomenclature global stiffness matrices element stiffness matrix width and height of a finite element ambient sound speed and density field-equation error vector components of the error vector forcing vector source frequency one- and two-dimensional basis functions a, b CQ,PO {E}