Research

Active Noise Control in Fluid Flows

Active Noise Control of Impingement Tones in Supersonic Aircraft Using MEMS

Organized structures often occur in fluid flows that possess a well-defined phase relationship. Such coherent structures can be found in many instances including (i) impinging jet flows, and (ii) flows past an open cavity. In both of these instances, strong acoustic signatures can be found that are generated through the interaction of acoustics with a shear-layer instability. The use of active control is a new and intriguing approach that is sought to modify the structure of the flow so as to result in a global alteration of its dominant features. In this regard, an innovative actuation method has been developed by our collaborator at FSU, which consists of introducing microjets along the periphery of the nozzle exit, thereby interrupting the shear-layer at its most receptive location and allowing the optimization of various performance metrics such as efficiency, flexibility, and robustness. The unique aspect that we have brought into this area is the realization of uniform and guaranteed improvement in the performance by using active control. By introducing the concept of closed-loop control into this problem, we have not only shown that it is possible to take actions on the basis of on-line measurements, but also that the closed-loop control shows an order of magnitude improvement (about 8db additional pressure reduction) over open-loop control actions [N1,N2]. Current project goals concern (i) development of reduced-order models that quantify the dominant interactions between the acoustics and the shear-layer that produce the underlying noise characteristics in the flow, (ii) development of closed-loop control strategies for manipulating the microjet flow so as to optimize its impact on the acoustics-shear layer interaction and deliver a robust performance over

Sponsors:

AFOSR (Unsteady Aerodynamics and Hypersonics Program)

Publications:

[N1] H. Lou, F. S. Alvi, C. Shih, J. Choi, and A. Annaswamy, "Active Control of Supersonic Impinging Jets: Flowfield Properties and Closed-loop Strategies", In AIAA 2002-2728, AIAA Flow Control Conference, June 2002.

[N2] A.M. Annaswamy, J. Choi, D. Sahoo, F. Alvi, and H. Lou, "Active Closed-loop Control of Supersonic Impinging Jet Flows Using POD models", IEEE Conference on Decision and Control, Las Vegas, NV, December 2002.

[N2b] Control of Supersonic Impinging Jetflows using Microjets ( Figures ), F.S. Alvi, R. Elavarasan, C. Shih, G. Garg, and A. Krothapalli, AIAA 2000-2236.






Movie

The Movie shows the flow-response when the microjets are turned off and on using the above time-profile. The response is repeated at heights h/D=3, 3.5, and 4. In all cases, the nozzle pressure ratio (NPR) was at five. The experiments were performed at the Fluid Mechanics Research Laboratory at FSU under the direction of Professors Farrukh Alvi and yulu Krothapalli.