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Acoustical modal analysis of the pressure field in the tailpipe of a turbofan engineThe results of a modal analysis of the pressure field in the tailpipe of a turbofan engine are presented. Modal amplitudes, at the tailpipe inlet and exit, are presented, as a function of frequency, for several operating conditions. The modal amplitudes were obtained using an optimization routine to obtain a best fit between measured cross spectra and an analytical expression for the cross spectra between pressures at circumferentially spaced locations. The measured pressure field was decomposed into a set of five modal amplitudes corresponding to the (0,0), (1,0), (2,0), (3,0), and (4,0) modes. The analysis was limited to frequencies below 1500 Hz where higher order modes are cutoff. The results of the analysis showed that at low frequencies, up to the cuton frequency of the (1,0) mode, the (0,0) mode (plane wave) dominated the pressure field. The frequency range from the cuton of the (1,0) mode to the cuton of the (2,0) mode was dominated by the (1,0) mode. The (2,0) mode dominated from its cuton frequency to the upper limit of the analysis, i.e., 1500 Hz. The contribution of modes other than the dominant mode was usually small.
Document ID
19830017228
Document Type
Conference Paper
Authors
Krejsa, E. A. (NASA Lewis Research Center Cleveland, OH, United States)
Karchmer, A. M. (NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 4, 2013
Publication Date
May 13, 1983
Subject Category
ACOUSTICS
Report/Patent Number
NAS 1.15:83387
E-1665
NASA-TM-83387
Meeting Information
Meeting of the Acoust. Soc. of Am.(Cincinnati)
Funding Number(s)
PROJECT: RTOP 506-31-32
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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