Abstract
A method for extracting the normal-incidence acoustic impedance of a test liner installed in the lower wall of a duct carrying a uniform flow was previously reported [W. R. Watson, M. G. Jones, and T. L. Parrott, AIAA paper No. 98-2279 (1998)]. This method has been extended to include the effects of shear flow and has been applied to data obtained for two dissimilar liners in the presence of grazing flow. The normal incidence impedance spectrum of the first liner was known to be flow independent while that of the second liner was expected to be flow dependent. A total pressure survey of the flow-impedance tube was performed to obtain an accurate description of the mean flow field in the vicinity of the liners. Acoustic data was obtained for a frequency range of 0.5–3.0 kHz and flow Mach numbers up to 0.5. Impedance spectra educed without flow for both liners reproduced that obtained experimentally in a normal-incidence impedance tube. As expected, when the grazing flow was turned on, the educed impedance spectra for the first liner showed no sensitivity to the grazing flow while that of the second liner was flow dependent.
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