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Measurement And Analyses Of The J57-P21 Noise Field

Report Number: AFFDL TR 66-147
Author(s): Hermes, P. H.; Smith, D. L.
Corporate Author: Air Force Flight Dynamics Laboratory
Laboratory: Air Force Flight Dynamics Laboratory
Date of Publication: 1966-10
Pages: 136
Contract: Laboratory Research - No Contract
Project: 1471
Task: 147102
AD Number: AD0648072

Abstract:
A noise survey of a J57-P21 turbojet engine was conducted to provide a basis for the development of a refined empirical noise prediction technique. The measurements were obtained at 65 locations for 5 engine power settings. The 1/3 octave and overall sound pressure levels (SPL's) for each location and engine power setting are presented. SPL contours are presented for overall and selected 1/3 octave bandwidths. Ground reflection effects on the 1/3 octave band SPL's are evaluated. Comparisons are made with other existing data. Differences of up to 15 decibels (db) are found when comparing the 1/3 octave band levels. Velocity exponents (n), based on the Lighthill parameter, are presented for each location and compared with existing data. Poor agreement is found among the measurement programs. The effect of ground reflection on the n values is investigated and an n field is presented in which interference effects are eliminated. The effect of varying noise directional properties with jet velocity on the n values is evaluated. An n field, corrected for both ground reflection and varying noise directional properties, is presented. This essentially constant n field clearly indicates the heavy dependence of the n values on noise directional changes with jet velocity. The corrected n field equation is considered the basis of a noise prediction method which appears to be accurate for jet flows with exit Mach numbers ranging from 0.5 to 2.0

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