Record Details

Noise Measurements of High Aspect Ratio Distributed Exhaust Systems
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Author and Affiliation:
Bridges, James E.(NASA Glenn Research Center, Cleveland, OH United States)
Abstract: This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly found in embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side (bevel) did produce up to 3 decibels more noise in all directions, while extending the lip on the narrow side (slant) produced up to 2 decibels more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron (notch) produced up to 2decibels increase in the noise. Having internal walls (septae) within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed electric propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.
Publication Date: Dec 01, 2015
Document ID:
20150023577
(Acquired Jan 05, 2016)
Subject Category: ACOUSTICS; AIRCRAFT PROPULSION AND POWER
Report/Patent Number: NASA/TM-2015-218901, E-19172, AIAA Paper 2015-3119, GRC-E-DAA-TN26436
Document Type: Technical Report
Publication Information: (SEE 20150022186)
Meeting Information: AIAA Aviation 2015 Conference ; 22-26 Jun. 2015; Dallas, TX; United States
Meeting Sponsor: American Inst. of Aeronautics and Astronautics; Reston, VA, United States
Contract/Grant/Task Num: WBS 110076.02.03.04.02
Financial Sponsor: NASA Glenn Research Center; Cleveland, OH United States
Organization Source: NASA Glenn Research Center; Cleveland, OH United States
Description: 24p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
NASA Terms: NOISE MEASUREMENT; ACOUSTIC MEASUREMENT; HIGH ASPECT RATIO; EXHAUST SYSTEMS; EXHAUST NOZZLES; NOZZLE GEOMETRY; EXHAUST VELOCITY; HIGH FREQUENCIES; ELECTRIC PROPULSION; NONINTRUSIVE MEASUREMENT; TRAILING EDGES; FAR FIELDS; DUCTS; JET AIRCRAFT NOISE
Other Descriptors: JET; AIRCRAFT; NOISE
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