Type of Document Thesis Author Sheehan, Michael Vincent Author's Email Address firstname.lastname@example.org URN etd-10032007-124143 Title Supersonic Flow and its Control Over Highly Three-Dimensional Cavities Degree Master of Science Department Mechanical Engineering, Department of Advisory Committee
Advisor Name Title Dr. Farrukh S. Alvi Committee Chair Dr. Lawrence Ukeiley Committee Member Dr. William Oates Committee Member Keywords
Date of Defense 2007-09-20 Availability unrestricted AbstractAn experimental study was undertaken whereby the effects of significant cavity three-dimensionalities on the flowfield and acoustic properties were addressed. A highly three-dimensional cavity having both diverging side walls, and a ramped floor, changing both the width and depth of the cavity, was tested and compared to a more simple rectangular model. The complex geometry should more realistically mimic real world applications, including aircraft weapons and cargo bays, whereas much of the published experimental research deals with purely rectangular cavity models. By testing both a highly complex geometry, and a simplified rectangular geometry, a direct comparison of the effect of the walls and floor was possible, allowing for the determination as to how accurate the rectangular cavity could model the acoustics of the much more complex model. It was found that to a first order the major components of the cavity acoustics including both the tonal frequencies, and the broadband noise levels, of the complex cavity were well predicted using the simple rectangular model. Some difference in the details was found in that the amplitude of the resonant tones in the rectangular model were much stronger. Finally an attempt was made to determine which of the geometrical features was having a dominant effect in changing of the cavity resonance. To accomplish this goal, two additional models were constructed each having only one of the additional geometrical features, either diverging side walls or the ramp floor. Subsequently it was determined that biggest impact on changing the cavity acoustics came from
the diverging side walls of the complex cavity.
In addition to testing the effect of cavity geometry, a microjet control technique was adapted to reduce the pressure loads within the highly three-dimensional cavity. An array consisting of eight 400micrometer diameter jets was used, and with minimal mass flow, reductions of both the tonal amplitudes and broadband levels was possible.
Along with testing on the very small scale, experiments were conducted with the same complex geometry nearly 10 times larger. Two major results were found: first the baseline, no control, acoustics of both the large and small models were found to scale quite well, moreover the microjet control technique was found to be similarly effective one the larger scale but with better efficiency. These results give good confidence that the aero-acoustic characteristics on a very small scale, as presented in this research, can be
used to accurately model full scale applications, and the further development of cavity control techniques.
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