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Investigation of continuously traversing microphone system for mode measurementThe continuously Traversing Microphone System consists of a data acquisition and processing method for obtaining the modal coefficients of the discrete, coherent acoustic field in a fan inlet duct. The system would be used in fan rigs or full scale engine installations where present measurement methods, because of the excessive number of microphones and long test times required, are not feasible. The purpose of the investigation reported here was to develop a method for defining modal structure by means of a continuously traversing microphone system and to perform an evaluation of the method, based upon analytical studies and computer simulated tests. A variety of system parameters were examined, and the effects of deviations from ideal were explored. Effects of traverse speed, digitizing rate, run time, roundoff error, calibration errors, and random noise background level were determined. For constant fan operating speed, the sensitivity of the method to normal errors and deviations was determined to be acceptable. Good recovery of mode coefficients was attainable. Fluctuating fan speed conditions received special attention, and it was concluded that by employing suitable time delay procedures, satisfactory information on mode coefficients can be obtained under realistic conditions. A plan for further development involving fan rig tests was prepared.
Document ID
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Cicon, D. E.
(Pratt and Whitney Aircraft Group East Hartford, CT, United States)
Sofrin, T. G.
(Pratt and Whitney Aircraft Group East Hartford, CT, United States)
Mathews, D. C.
(Pratt and Whitney Aircraft Group East Hartford, CT, United States)
Date Acquired
September 4, 2013
Publication Date
November 1, 1982
Subject Category
Report/Patent Number
NAS 1.26:168040
Accession Number
Funding Number(s)
PROJECT: RTOP 505-31-32
Distribution Limits
Work of the US Gov. Public Use Permitted.
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