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Subharmonic and fundamental high amplitude excitation of an axisymmetric jetA circular jet was excited simultaneously by two different harmonically related tones. Data for three pairs of Strouhal numbers (St(D) = f*D/U (sub j) = 0.2 and 0.4, 0.3 and 0.6, 0.4 and 0.8). For each case the initial phase difference between the two waves was varied in steps of 45 deg, for one full cycle and the level of the fundamental and subharmonic forcing were varied independently over the range of 0.1 to 7 percent of the jet exit velocity. Our initial findings concurred with published findings, such as a critical level of the fundamental is required for subharmonic augmentation, the initial phase difference is critical in determining whether the subharmonic is augmented or suppressed. The detailed documentation of several aspects of this phenomenon all measured in one and the same experimental facility in a controlled manner, bring out several important points that eluded previous researchers: (1) At high amplitudes of the fundamental and subharmonic forcing levels the subharmonic augmentation is independent of the initial phase difference. (2) Contrary to the earlier belief that stable pairing could be produced only with an initial laminar boundary layer, the present work shows that by the two-frequency excitation method this phenomenon can be induced over a range of conditions for a jet with an initially turbulent boundary layer. (3) It is seen that two-frequency excitation is indeed more effective than single frequency excitation in jet mixing enhancement. Higher spreading rates seem to go along with higher subharmonic levels.
Document ID
19890011549
Document Type
Technical Memorandum (TM)
Authors
Raman, Ganesh (Sverdrup Technology, Inc., Cleveland OH., United States)
Rice, Edward J. (NASA Lewis Research Center Cleveland, OH., United States)
Date Acquired
September 5, 2013
Publication Date
March 1, 1989
Subject Category
AERODYNAMICS
Report/Patent Number
NAS 1.15:101946
AIAA PAPER 89-0993
E-4595
NASA-TM-101946
Meeting Information
Shear Flow Conference(Tempe, AZ)
Funding Number(s)
PROJECT: RTOP 505-62-21
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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