NDLI: Spinning mode sound propagation in ducts with acoustic treatment (Document No: 19750015175)

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Spinning mode sound propagation in ducts with acoustic treatment (Document No: 19750015175)

Content Provider	NASA Technical Reports Server (NTRS)
Author	Rice, E. J.
Copyright Year	1975
Description	Recent acoustic data show larger noise attenuations than predicted for acoustically treated aircraft engine inlets without splitter rings. A theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts is presented, and a suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. Theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. Results of the analysis indicate that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number, and for annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. These results explain why suppressors with splitter rings were quite effective in spite of the lack of detailed information on the noise source modal structure. Conversely, effective use of outer wall treatment alone will require expanded knowledge of the noise source structure. Approximate solutions are presented to help interpret the more exact theoretical results.
File Size	1408824
Page Count	32
File Format	PDF
Alternate Webpage(s)	http://archive.org/details/NASA_NTRS_Archive_19750015175
Archival Resource Key	ark:/13960/t3gx93454
Language	English
Publisher Date	1975-05-01
Access Restriction	Open
Subject Keyword	Acoustics Sound Propagation Noise Reduction Mathematical Models Nose Inlets Acoustic Ducts Bessel Functions Acoustic Attenuation Suppressors Mach Number Propagation Modes Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science
Content Type	Text
Resource Type	Technical Report

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