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Distributed Exhaust Nozzles for Jet Noise ReductionThe main objective of this study is to validate the jet noise reduction potential of a concept associated with distributed exhaust nozzles. Under this concept the propulsive thrust is generated by a larger number of discrete plumes issuing from an array of small or mini-nozzles. The potential of noise reduction of this concept stems from the fact that a large number of small jets will produce very high frequency noise and also, if spaced suitably, they will coalesce at a smaller velocity to produce low amplitude, low frequency noise. This is accomplished through detailed acoustic and fluid measurements along with a Computational Fluidic Dynamic (CFD) solution of the mean (DE) Distributed Exhaust nozzle flowfield performed by Northrop-Grumman. The acoustic performance is quantified in an anechoic chamber. Farfield acoustic data is acquired for a DE nozzle as well as a round nozzle of the same area. Both these types of nozzles are assessed numerically using Computational Fluid Dynamic (CFD) techniques. The CFD analysis ensures that both nozzles issued the same amount of airflow for a given nozzle pressure ratio. Data at a variety of nozzle pressure ratios are acquired at a range of polar and azimuthal angles. Flow visualization of the DE nozzle is used to assess the fluid dynamics of the small jet interactions. Results show that at high subsonic jet velocities, the DE nozzle shifts its frequency of peak amplitude to a higher frequency relative to a round nozzle of equivalent area (from a S(sub tD) = 0.24 to 1. 3). Furthermore, the DE nozzle shows reduced sound pressure levels (as much as 4 - 8 dB) in the low frequency part of the spectrum (less than S(sub tD) = 0.24 ) compared to the round nozzle. At supersonic jet velocities, the DE nozzle does not exhibit the jet screech and the shock-associated broadband noise is reduced by as much as 12 dB.
Document ID
20020016714
Acquisition Source
Glenn Research Center
Document Type
Other
Authors
Ahuja, K. K. (Georgia Tech Research Inst. Atlanta, GA United States)
Gaeta, R. J. (Georgia Tech Research Inst. Atlanta, GA United States)
Hellman, B. (Georgia Tech Research Inst. Atlanta, GA United States)
Schein, D. B. (Northrop Grumman Corp. El Segundo, CA United States)
Solomon, W. D., Jr. (Northrop Grumman Corp. El Segundo, CA United States)
Huff, Dennis
Date Acquired
September 7, 2013
Publication Date
December 31, 2001
Subject Category
Aircraft Propulsion And Power
Report/Patent Number
GTRI-Rept-A6221/2001-1
Funding Number(s)
CONTRACT_GRANT: NAG3-2352
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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