GLTRS--Glenn
TITLE AND SUBTITLE:
Effects of Acoustically Lined Cylindrical Ducts on Instability Waves in Confined Supersonic Jets

AUTHOR(S):
Milo D. Dahl

REPORT DATE:
May 1997

FUNDING NUMBERS:
WU-505-62-52

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191

PERFORMING ORGANIZATION REPORT NUMBER:
E-10709

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Washington, DC 20546-0001

REPORT TYPE AND DATES COVERED:
Technical Memorandum

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA TM-107441
AIAA-97-1600

SUPPLEMENTARY NOTES:
Prepared for the Third Aeroacoustics Conference sponsored by the American Institute of Aeronautics and Astronautics and the Confederation of European Aerospace Societies, Atlanta, Georgia, May 12-14, 1997. Responsible person, Milo D. Dahl, organization code 2660, (216) 433-3578.

ABSTRACT:
The pressure disturbances generated by an instability wave in the shear layer of a supersonic jet are studied for an axisymmetric jet inside a lined cylindrical duct. For the supersonic jet, locally linear stability analysis with duct wall boundary conditions is used to calculate the eigenvalues and the eigenfunctions. These values are used to determine the growth rates and phase velocities of the instability waves and the radial pressure disturbance patterns. The study is confined to the dominant Kelvin-Helmholtz instability mode and to the region just downstream of the nozzle exit where the shear layer is growing but is still small in size compared to the radius of the duct. Numerical results are used to study the effects of changes in the outer flow, growth in the shear layer thickness, wall distance, wall impedance, and frequency. Results indicate that the effects of the duct wall on shear layer growth rates diminish as the outer flow increases. Also, wall reflections cause variations in growth rates depending on wall height and Strouhal number. These variations are due to the phase relationship between the outgoing and the reflected incoming pressure disturbances at the shear layer. The growth rate variations can be reduced and the maximum growth rate minimized by keeping the imaginary part of the impedance negative.

SUBJECT TERMS:
Supersonic jets; Acoustic treatment; Instability waves; Ejectors; Confined jets

NUMBER OF PAGES:
13

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1997/TM-107441.pdf
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