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Abstract:
Supersonic impinging jet flows, such as those that occur in the next generation of STOVL aircraft, are highly unsteady due to the presence a feedback loop. This results in large dynamic loads on the nearby aircraft structures and surfaces and diminishes aircraft performance. In this study, a unique active control technique that utilizes arrays of supersonic microjets (less than or equal 400 micrometers) around the periphery of the main jet was examined. The efficacy of microjet control was explored over a large parametric range. This control approach was very successful and the activation of the microjets led to dramatic reductions in ground effect. The lift loss was reduced by up to 40%, while the unsteady loads were reduced by as much as 12 dB. These dramatic gains in performance were achieved with negligible microjet mass flux (less than 0.5%) . A detailed study of this flow was conducted to better understand the governing flow physics. The velocity field data clearly indicates that the activation of microjets generates significant streamwise vorticity while reducing the azimuthal vorticity of the primary jet It is proposed that the streamwise vorticity is mainly a result of the redirection of the azimuthal vorticity, which weakens the large-scale structures in the primary jet. This is considered to be a primary factor in the efficient disruption of the feedback loop. A new, POD-based, closed-loop control strategy, is also explored in order to achieve optimal and uniform control. The closed-loop control results led to an improvement in the control efficiency compared to the open-loop strategy in a number of cases.
| Limitations: |
 APPROVED FOR PUBLIC RELEASE |
| Description: |
Final rept. Jan 2000-Apr 2003 |
| Pages: |
144 |
| Report Date: |
28 APR 2003 |
| Contract Number: |
F49620-00-1-0141 |
| Report Number: |
A419414 |
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