Acoustic Holography Mapping of Jet Plumes – 03/17/08
The Air Force Research Laboratory selected Blue Ridge Research and Consulting (BRRC) to develop innovative measurement and analysis methods to characterize and map the noise emitted from jet engines. Funding was provided through a Phase II Award under the Small Business Innovation Research (SBIR) program.
Background
The current and next-generation military jet aircraft expose ground maintenance personnel and the surrounding community to high levels of noise. In response, the DoD is funding research to develop advanced modeling tools for community noise exposure and for noise reduction techniques. However, a limiting factor in tool development was identified: insufficient understanding of the jet noise source. Traditional measurement methods cannot adequately characterize the complex structure and content of the jet noise plume. For these tools to achieve their full potential in addressing the noise problem, innovative measurement and analysis methods are necessary.
Approach
To meet the need for better military jet noise source characterization, BRRC and Brigham Young University developed an aircraft jet plume source noise measurement system. The system uses near-field acoustical holography (NAH) measurements to visualize the sound field in the jet exhaust region, and leverages a patch and scan measurement approach with a ninety channel microphone array and over fifty reference microphones to detail the magnitude, directivity, spectral content, and spatial distribution of the jet noise. The 2 feet by 8 ½ feet planar surface of the microphone array can be moved from the jet nozzle down the plume to make pressure measurements, with the reference microphones located parallel to the nozzle center line.
Results
The NAH system was tested on an F-22 fighter jet, shown below on afterburner power. The resulting acoustic source definition can be used to improve predictions of ground personnel noise exposure, evaluate the performance of proposed noise control devices, and provide model refinement and benchmarking.
Awards & Recognition
Michael James and Dr. Kent Gee, BRRC Vice President and Brigham Young University Assistant Professor of Physics, respectively, were recently recognized with National Instruments’ top Award for Machine Control and Monitoring for their contribution to the development of the NAH system. In addition, the NAH system was featured as the cover story for the September 2010 edition of Sound and Vibration magazine entitled, “Aircraft Jet Plume Source Noise Measurement System”.
NAH Measurement Array Recording Noise Generated from an F-22 on Afterburner Engine Power*
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Conceptual Image of the Test Rig Structure
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Vertical Configuration |
Overall Measured Sound Pressure Level from an F-22 on Afterburner Engine Power
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Partner: Brigham Young University Acoustics Research Group
Sponsor: Air Force Research Laboratory - Wright-Patterson AFB, OH |
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