Conventional aircraft typically include propulsion engines that are under the wing or tail surfaces. Each propulsion engine system includes an engine housed in a nacelle with an inlet and a nozzle system. Primary component noise sources from the engine system include the noise associated with the fan, compressor, turbine, and combustor, and the noise associated with the high-velocity jet exhaust flow. There are many methods for reducing the various noise sources from the aircraft, including those noise sources from the engine system. One method includes the use of the aircraft itself as an acoustic shield for the noise sources associated with the engines. This approach requires a new configuration of aircraft with the engines installed on the upper surface of the wing or fuselage, or an aircraft that has a hybrid wing and fuselage. Of the engine noise sources, the jet exhaust is a particular challenge due to the fact that the noise sources are in the exhaust flow itself, and therefore originate throughout the jet exhaust flow as many as ten engine diameters downstream of the nozzle system exit plane. Therefore, it is desirable to have an improved aircraft nozzle system that is capable of much more noise reduction when installed on the upper surface of the aircraft.

This invention accomplishes this objective by providing an aircraft engine exhaust system that can reduce noise simultaneously through three approaches. The invention can reduce low-frequency jet noise, a source that is more difficult to shield by the aircraft. It can also redistribute the peak noise sources over a broad frequency range upstream toward the nozzle so that they can be more effectively shielded by the aircraft. And finally, depending on the embodiment, the invention can redistribute jet noise sources in the azimuthal direction so that peak direction of propagation is away from the region of interest.

The present invention is an engine exhaust nozzle system for an aircraft. Several embodiments of the present invention include the nozzle system as being a separate flow, round, or chevronformed nozzle system installed above the wing, tail surfaces, or fuselage of the aircraft, or within a hybrid wing body aircraft where the engine is installed above the wing. Embodiments of the invention include the use of pylon technology to increase the effectiveness of acoustic shielding in the aircraft, and modifying the orientation of the nozzle system and the pylon technology to even further increase the effectiveness of acoustic shielding.

The nozzle system redistributes engine noise sources upstream where they can be shielded by a surface of the aircraft. Therefore, it reduces noise associated with the engine exhaust by increasing the effectiveness of acoustic shielding by the aircraft. The system may be applied to other industries; for example, a high-pressure exhaust duct from a factory, machinery, or other applications to reduce associated noise.

This work was done by Russell H. Thomas, Michael J. Czech, and Ronen Elkoby of Langley Research Center. NASA is actively seeking licensees to commercialize this technology. Please contact LaRCPatentLicensing@ to initiate licensing discussions. Follow this link for more information: . LAR-17832-1

NASA Tech Briefs Magazine

This article first appeared in the May, 2016 issue of NASA Tech Briefs Magazine.

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