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Asheville, NC, United States

Neilsen T.B.,Brigham Young University | Gee K.L.,Brigham Young University | Wall A.T.,Brigham Young University | James M.M.,Blue Ridge Research and Consulting
Journal of the Acoustical Society of America | Year: 2013

Noise measured in the vicinity of an F-22A Raptor has been compared to similarity spectra found previously to represent mixing noise from large-scale and fine-scale turbulent structures in laboratory-scale jet plumes. Comparisons have been made for three engine conditions using ground-based sideline microphones, which covered a large angular aperture. Even though the nozzle geometry is complex and the jet is nonideally expanded, the similarity spectra do agree with large portions of the measured spectra. Toward the sideline, the fine-scale similarity spectrum is used, while the large-scale similarity spectrum provides a good fit to the area of maximum radiation. Combinations of the two similarity spectra are shown to match the data in between those regions. Surprisingly, a combination of the two is also shown to match the data at the farthest aft angle. However, at high frequencies the degree of congruity between the similarity and the measured spectra changes with engine condition and angle. At the higher engine conditions, there is a systematically shallower measured high-frequency slope, with the largest discrepancy occurring in the regions of maximum radiation. © 2013 Acoustical Society of America. Source

Wall A.T.,Brigham Young University | Gee K.L.,Brigham Young University | Neilsen T.B.,Brigham Young University | Krueger D.W.,Brigham Young University | James M.M.,Blue Ridge Research and Consulting
Journal of the Acoustical Society of America | Year: 2014

Near-field acoustical holography methods are used to predict sound radiation from an engine installed on a high-performance military fighter aircraft. Cylindrical holography techniques are an efficient approach to measure the large and complex sound fields produced by full-scale jets. It is shown that a ground-based, one-dimensional array of microphones can be used in conjunction with a cylindrical wave function field representation to provide a holographic reconstruction of the radiated sound field at low frequencies. In the current work, partial field decomposition methods and numerical extrapolation of data beyond the boundaries of the hologram aperture are required prior to holographic projection. Predicted jet noise source distributions and directionality are shown for four frequencies between 63 and 250Hz. It is shown that the source distribution narrows and moves upstream, and that radiation directionality shifts toward the forward direction, with increasing frequency. A double-lobe feature of full-scale jet radiation is also demonstrated. © 2014 Acoustical Society of America. Source

James M.M.,Blue Ridge Research and Consulting | Gee K.L.,Brigham Young University
Sound and Vibration | Year: 2010

Jet engine technology is more sophisticated than ever, building on decades of learning and growth in the field. However, even the latest advances in jet engine design and technology have not been able to counter an age-old challenge - noise. Noise issues persist and adversely impact both ground maintenance personnel and surrounding communities. There is continued research to combat this issue, but for these emerging tools to achieve their full potential, innovative measurement and analysis methods are necessary to characterize the jet noise source region. A near-field acoustic holography system has been developed to meet this need and provide high-quality acoustic data. These data can be used for model refinement and benchmarking, evaluation of noise control devices, and predicting ground maintenance personnel and community noise exposure. The design of the 150-channel measurement array and data acquisition system is presented here. The prototype system was used recently to perform jet source noise measurements of an F-22 at Holloman Air Force Base located near Alamogordo, NM. The measurement approach and sound pressure level measurement maps detailing the near-field levels, spatial extent, and frequency content for four power conditions are featured. Source

Downing M.,Blue Ridge Research and Consulting
Proceedings of Meetings on Acoustics | Year: 2013

Recent research efforts on nonlinear propagation from high performance jet aircraft have revealed an interesting challenge to predicting community response. This challenge focuses on receiver perception of these unique acoustical signals, which contain acoustical shocks that appear to increase their relative loudness and/or noisiness. This current finding suggests a need for an improved description of a receiver perception of the loudness of these signals in order to improve the assessment of noise impacts from these aircraft. Looking backwards, an interesting question emerges: did the earlier low bypass jet engines on commercial and transport aircraft also include these acoustical shocks? If they did contain these features, then the perceptual differences observed between aircraft and other transportation noise sources may be partially explained. © 2013 Acoustical Society of America. Source

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2015

ABSTRACT:The proposed effort will begin connecting military jet noise source and field properties with waveform and spectral features that correlate with human perception and annoyance. Tactical military aircraft noise evokes significant community response relative to ordinary transportation noise because of its high amplitudes and unique features, such as significant shock content and low-frequency rumble. During Phase I, metrics will be examined for ability to correlate physical noise characteristics, such as source distribution, radiation properties, directivity, and shock content, with human annoyance and disturbance. A comprehensive evaluation of existing tactical jet noise measurement databases will be conducted to determine their suitability for Phase-II listener studies based on candidate metrics. The listener test experimental design, training protocols, and reviews will be completed. Experimental design for any additional required acoustical measurements will also be developed. To guide source characterization efforts and improve ability to extract significant noise features, a cost/benefit analysis of acoustical holography and beamforming will be conducted with full-scale data. These technical tasks will lay the foundation for quantifying source and field features that impact human perception in Phase II. The results will improve prediction of community noise impacts and guide future noise models, data collection, and noise mitigation efforts.BENEFIT:The teams combined experience in the areas of aircraft noise measurements, noise model development, and environmental impact determination associated with operations of military aircraft demonstrate a unique ability to assess the market need for this research and its utility and benefits to the community at large. In addition to a continuous effort to publish new and relevant research, active participation in multiple conferences each year, and numerous connections to both government and commercial clients provide us with the ability to increase awareness of this technology and market through a multitude of avenues. With the beddown of the next-generation of fighter jets such as the F 35, the demand for improved metrics that correlate jet noise exposure to human response and the desire for increased understanding of jet noise source characterization is only expected to increase,. The specialized jet noise metrics developed under this effort will attempt to represent the psychoacoustic response to high-power jet noise, which will improve in the evaluation of community impacts. Evaluating potential environmental impacts, including noise, is required by the National Environmental Protection Act (NEPA) for proposed actions, such as the beddown of the F-35. The environmental impact from aircraft are currently evaluated by the DOD, FAA, and other federal agencies using models such as NOISEMAP and AEDT, which output traditional noise metrics. Through the development of these specialized metrics, identification of the temporal and spectral jet noise characteristics associated with human response will inform requirements to improve and refine the sound propagation models used to evaluate community impacts. These advancements will lead to a deeper understanding of the community responds to jet noise and will improve the overall environment assessment of community noise exposures from tactical jet operations. These improved tools will translate into better relationships between the airfield and neighboring communities. Additionally, these specialized metrics are anticipated to play a crucial role in rocket noise impact evaluation from the emerging spaceport industry, regulated by FAA/AST, NASA, and the Air Force. Improved jet noise source characterization and a deeper understanding of jet noise generation mechanisms will inform future aircraft noise measurements. A high-fidelity representation of the noise sources will provide better inputs to environmental noise models, mission planning tools, and research tools than currently available. The acoustic source definitions, refined under this effort, will be used to improve predictions of ground personnel noise exposure, evaluate the performance of proposed noise control devices, and provide model refinement and benchmarking.

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