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Core noise source diagnostics on a turbofan engine using correlation and coherence techniquesFluctuating pressure measurements at several locations within the core of a turbofan engine were made simultaneously with far field acoustic measurements. Correlation and coherence techniques were used to determine the relative amplitude and phase relationships between core pressures at these various locations and between the core pressures and far field acoustic pressure. The combustor is a low frequency source region for acoustic propagation through the core nozzle and out to the far field. The relation between source pressure and the resulting sound pressure involves a 180 degree phase shift and an amplitude transfer function which varies approximately as frequency squared. This is consistent with a simplified model using fluctuating entropy as a source term.
Document ID
19770004110
Document Type
Conference Paper
Authors
Karchmer, A. M. (NASA Lewis Research Center Cleveland, OH, United States)
Reshotko, M. (NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 3, 2013
Publication Date
January 1, 1976
Subject Category
AIRCRAFT PROPULSION AND POWER
Report/Patent Number
NASA-TM-X-73535
E-8961
Meeting Information
Meeting of the Acoust. Soc. of Am.(San Diego, CA)
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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