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Effects of Mean Flow Assumption and Harmonic Distortion on Impedance Eduction Methods

2014; American Institute of Aeronautics and Astronautics; Volume: 53; Issue: 6 Linguagem: Inglês

10.2514/1.j053399

1533-385X

Michael G. Jones, Willie R. Watson, Brian M. Howerton, Stefan Busse-Gerstengarbe,

Computational Fluid Dynamics and Aerodynamics

This investigation uses methods based on the Pridmore-Brown and convected Helmholtz equations to study the acoustic behavior of a single-layer, conventional liner fabricated by DLR, German Aerospace Center and tested in the NASA Langley Grazing Flow Impedance Tube. Two key assumptions are explored in this investigation. First, a comparison of results achieved with uniform-flow and shear-flow impedance eduction methods is considered. Second, an approach based on the Prony method is used to extend these methods from single-mode to multimode implementations. In addition, a detailed study into the effects of harmonic distortion on the educed impedance is performed, and the results are used to develop guidelines regarding acceptable levels of harmonic distortion.