NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
A Numerical Theory for Impedance Education in Three-Dimensional Normal Incidence TubesA method for educing the locally-reacting acoustic impedance of a test sample mounted in a 3-D normal incidence impedance tube is presented and validated. The unique feature of the method is that the excitation frequency (or duct geometry) may be such that high-order duct modes may exist. The method educes the impedance, iteratively, by minimizing an objective function consisting of the difference between the measured and numerically computed acoustic pressure at preselected measurement points in the duct. The method is validated on planar and high-order mode sources with data synthesized from exact mode theory. These data are then subjected to random jitter to simulate the effects of measurement uncertainties on the educed impedance spectrum. The primary conclusions of the study are 1) Without random jitter the method is in excellent agreement with that for known impedance samples, and 2) Random jitter that is compatible to that found in a typical experiment has minimal impact on the accuracy of the educed impedance.
Document ID
20160009105
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Watson, Willie R.
(NASA Langley Research Center Hampton, VA, United States)
Jones, Michael G.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
July 17, 2016
Publication Date
May 30, 2016
Subject Category
Acoustics
Report/Patent Number
NF1676L-22697
Meeting Information
Meeting: AIAA/CEAS Aeroacoustics Conference
Location: Lyon
Country: France
Start Date: May 30, 2016
End Date: June 1, 2016
Sponsors: American Inst. of Aeronautics and Astronautics, Council of European Aerospace Societies
Funding Number(s)
WBS: WBS 081876.02.07.03
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
No Preview Available