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Limitations of Phased Array Beamforming in Open Rotor Noise Source ImagingPhased array beamforming results of the F31/A31 historical baseline counter-rotating open rotor blade set were investigated for measurement data taken on the NASA Counter-Rotating Open Rotor Propulsion Rig in the 9- by 15-Foot Low-Speed Wind Tunnel of NASA Glenn Research Center as well as data produced using the LINPROP open rotor tone noise code. The planar microphone array was positioned broadside and parallel to the axis of the open rotor, roughly 2.3 rotor diameters away. The results provide insight as to why the apparent noise sources of the blade passing frequency tones and interaction tones appear at their nominal Mach radii instead of at the actual noise sources, even if those locations are not on the blades. Contour maps corresponding to the sound fields produced by the radiating sound waves, taken from the simulations, are used to illustrate how the interaction patterns of circumferential spinning modes of rotating coherent noise sources interact with the phased array, often giving misleading results, as the apparent sources do not always show where the actual noise sources are located. This suggests that a more sophisticated source model would be required to accurately locate the sources of each tone. The results of this study also have implications with regard to the shielding of open rotor sources by airframe empennages.
Document ID
Acquisition Source
Glenn Research Center
Document Type
Technical Memorandum (TM)
Horvath, Csaba
(ASRC Aerospace Corp. Cleveland, OH, United States)
Envia, Edmane
(NASA Glenn Research Center Cleveland, OH, United States)
Podboy, Gary G.
(NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
April 8, 2014
Publication Date
August 1, 2013
Subject Category
Report/Patent Number
Meeting Information
Meeting: Aeroacoustics Conference
Location: Berlin
Country: Germany
Start Date: May 27, 2013
End Date: May 29, 2013
Sponsors: American Inst. of Aeronautics and Astronautics, Confederation of European Aerospace Societies
Funding Number(s)
WBS: WBS 699959.
Distribution Limits
Public Use Permitted.
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