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Numerical and Experimental Determination of the Geometric Far Field for Round JetsTo reduce ambiguity in the reporting of far field jet noise, three round jets operating at subsonic conditions have recently been studied at the NASA Glenn Research Center. The goal of the investigation was to determine the location of the geometric far field both numerically and experimentally. The combination of the WIND Reynolds-Averaged Navier-Stokes solver and the MGBK jet noise prediction code was used for the computations, and the experimental data was collected in the Aeroacoustic Propulsion Laboratory. While noise sources are distributed throughout the jet plume, at great distances from the nozzle the noise will appear to be emanating from a point source and the assumption of linear propagation is valid. Closer to the jet, nonlinear propagation may be a problem, along with the known geometric issues. By comparing sound spectra at different distances from the jet, both from computational methods that assume linear propagation, and from experiments, the contributions of geometry and nonlinearity can be separately ascertained and the required measurement distance for valid experiments can be established. It is found that while the shortest arc considered here (approx. 8D) was already in the geometric far field for the high frequency sound (St greater than 2.0), the low frequency noise due to its extended source distribution reached the geometric far field at or about 50D. It is also found that sound spectra at far downstream angles does not strictly scale on Strouhal number, an observation that current modeling does not capture.
Document ID
20030055692
Acquisition Source
Glenn Research Center
Document Type
Other
Authors
Koch, L. Danielle (NASA Glenn Research Center Cleveland, OH, United States)
Bridges, James (NASA Glenn Research Center Cleveland, OH, United States)
Brown, Cliff (NASA Glenn Research Center Cleveland, OH, United States)
Khavaran, Abbas (QSS Group, Inc. Cleveland, OH, United States)
Date Acquired
September 7, 2013
Publication Date
May 1, 2003
Subject Category
Acoustics
Report/Patent Number
E-13956
Meeting Information
Meeting: Noise-Con 2003
Location: Cleveland, OH
Country: United States
Start Date: June 23, 2003
End Date: June 25, 2003
Sponsors: Institute of Noise Control Engineering
Funding Number(s)
WBS: WBS 22-781-30-12
Distribution Limits
Public
Copyright
Public Use Permitted.

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