|Date||February 6, 2013||Time||12:20 - 2:00 pm|
|Location||Rogers Engineering & Computer Science Building Room 106|
|Description||Dr. Charles E. Tinney|
Department of Aerospace Engineering and Engineering Mechanics
University of Texas at Austin
"Cumulative nonlinear distortion of acoustic waves produced by high-speed jet flows"
In supersonic jets, an extended line of distributed sources act in compliance to generate and propagate noise in a complex manner to an observer far away from the jet. Nonlinear distortion of the acoustic waveform is often considered a prerequisite to understanding this propagation process. This is driven by one's capture of 'shock-type' structures or so called 'N-wave' type signatures in the pressure waveform, which are generally attributed to nonlinear wave steepening. Likewise, imperfect collapse of the spectra between an observer signal and a prediction, formed from a linear rescaling of the closer signal (using 1/r2 dependence), is also believed to be caused by nonlinear distortion. Unfortunately, these observations are most often made using measurements acquired in a range-restricted environment where changes to the waveform, due to cumulative nonlinear distortion, are too small to be accurately quantified, and/or without prior knowledge of the sound propagation path. The current work aims to fill this gap by exploring the acoustic field produced by an unheated, perfectly expanded, Mach 3 jet in a laboratory-scale environment. This talk focuses on a time-averaged approach to understanding the degree of non-linearity in the acoustic waveform at several far-field observer positions. Various "off-the-shelf" indicators are explored including a new model for predicting the presence (or lack there of) of cumulative non-linear waveform distortions in the signal.
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