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Accurate measurement of the noise fields emitted by a full scale high performance jet engine and jet plume (with supersonic jet flow) requires detailed planning and careful execution. The apparent acoustic source can be very large, more than 50 feet long and 20 feet high and wide. The jet plume contains many noise generating sources, the main two being shock (broad band and shock cells) and turbulent mixing. This paper is an initial description of a detailed method to accurately measure and describe the near-field noise while simultaneously measuring the far-field noise. For a large high performance jet engine, the acoustic far-field may not be formed until more than 1000 ft away from the plume. The paper also describes proposed methods to measure the non-linear propagation of the noise from the near-field to the far-field. The proposed methodology described with vetting will be considered as an US military standard (MILSTD) with possible later consideration as American standard measurement technique to describe noise fields for personnel noise exposure and for measuring the performance of jet engine noise reduction technologies.

In April 1994, the USAF Armstrong Laboratory, in cooperation with USAF Test Pilot School, conducted an experimental study of controlled focus boom generated by supersonic maneuvers. The objective of this study was to collect focus and postfocus booms and to assess the ability of aircrews to control the placement of the focal region during basic maneuvers. Forty-nine supersonic passes were flown and included level linear acceleration, level turn, accelerating dives, and climbout-pushover maneuvers. These flights were flown under calm and turbulent atmospheric conditions. Turbulent conditions had a defocusing effect which caused distortions in the focus region and resulted in smaller maximum overpressures. Sonic booms were collected by up to 25 boom event analyzer recorders (BEARs) placed in a 13 000-ft linear array. The BEAR units were spaced 500–2000 ft apart with the denser spacing at the expected focal region. This spacing was chosen to evaluate the thickness of both the focal and postfocal regions. The target location varied from 2000–5000 from the uptrack end of the array. Of the 49 flights, a focus boom was placed within the array 37 times and within ±3000 feet of the target point 27 times, demonstrating the ability to place controlled focus booms.

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