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Abstract
Military jet aircraft generate high levels of noise which require innovative measurement and analysis methods to characterize the jet noise. A near-field acoustic holography (NAH) system is being developed to provide model refinement and benchmarking, evaluate performance of noise control devices, and predict ground maintenance personnel and community noise exposure. A prototype NAH system was used to perform jet source noise measurements of an F-22 at Holloman AFB, NM. This NAH system utilizes a patch and scan measurement approach using a 90 channel microphone array and over 50 reference microphones. The microphone array was used to make pressure measurements on a planar surface extending from the jet nozzle to 75 ft along the plume and over 6 ft in height. These measurements were made parallel either to the shear layer or to the nozzle center line of the jet plume at three different offset distances. Measurements were made every 6 in. on the surface which results in over 1800 measurements per offset distance. The ground based fixed reference microphones were located parallel to the nozzle center line. The measurement approach and pressure measurements for four power conditions detailing the source size, frequency content, and ground effect will be detailed. [Work supported by AFRL SBIR.]
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