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AXISYMMETRICAL JET FORCED BY FUNDAMENTAL AND SUBHARMONIC TONES
Title
AXISYMMETRICAL JET FORCED BY FUNDAMENTAL AND SUBHARMONIC TONES
Creator
Raman, G, Rice, Ej
Date
1991-07
Publisher
AMER INST AERONAUT ASTRONAUT
Description
A circular jet was excited simultaneously by two harmonically related tones. The results of this excitation on jet behavior are reported for...
Show moreA circular jet was excited simultaneously by two harmonically related tones. The results of this excitation on jet behavior are reported for three pairs of Strouhal numbers [St(D) = f*D/U(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 tones was varied in steps of 45 deg for one full cycle, and the amplitude of the fundamental and subharmonic tones was varied independently over the range of 0.1-7.0% of the jet exit velocity. Several results of this study agreed with other published findings, such as a critical amplitude or the fundamental being required for subharmonic augmentation and the initial phase difference being critical in determining whether the subharmonic is augmented or suppressed. In addition, the detailed documentation or several aspects of this phenomenon, measured in the same experimental facility in a controlled manner, brought out two important points that had eluded previous researchers. First, at high levels of the fundamental and subharmonic forcing amplitudes, the subharmonic augmentation is independent of the initial phase difference. Second, 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.
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Resonant interaction of a linear array of supersonic rectangular jets: An experimental study
Title
Resonant interaction of a linear array of supersonic rectangular jets: An experimental study
Creator
Raman, G, Taghavi, R
Date
1996-02-25
Publisher
CAMBRIDGE UNIV PRESS
Description
This paper examines a supersonic multi-jet interaction problem that we believe is likely to be important for mixing enhancement and noise...
Show moreThis paper examines a supersonic multi-jet interaction problem that we believe is likely to be important for mixing enhancement and noise reduction in supersonic mixer-ejector nozzles. We demonstrate that it is possible to synchronize the screech instability of four rectangular jets by precisely adjusting the inter-jet spacing. Our experimental data agree with a theory that assumes that the phase-locking of adjacent jets occurs through a coupling at the jet lip. Although synchronization does not change the frequency of the screech tone, its amplitude is augmented. The synchronized multi-jets exhibit higher spreading than the unsynchronized jets, with the single jet spreading the least. We compare the near-field noise of the four jets with synchronized screech to the noise of the sum of four jets operated individually. Our noise measurements reveal that the more rapid mixing of the synchronized multi-jets causes the peak jet noise source to move upstream and to radiate noise at larger angles to the flow direction. Based on our results, we have grounds to believe that screech synchronization is advantageous for noise reduction internal to a mixer-ejector nozzle, since the noise can now be suppressed by a shorter acoustically lined ejector.
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