Localized arc filament plasma actuators have been used to control pressure fluctuations in a cavity with a length to depth ratio of 4.86. The rear wall of the cavity is inclined 30° above the horizontal plane and the cavity length is 61.7 mm, measured from the leading edge of the cavity to the mid-plane of the ramp. Five actuators have been uniformly distributed along the span of the wind tunnel at 1 mm upstream to the cavity leading edge. Experiments were conducted at Mach 0.6 and a Reynolds number of approximately 2x105 based on cavity depth. Forcing was conducted quasi-two-dimensionally and three-dimensionally. With this Mach number and geometry, the cavity was strongly resonating at the 2nd Rossiter mode corresponding to a frequency of 2.5 kHz.
Time-resolved pressure measurements were used to assess the effectiveness of the actuators. Forcing quasi-two-dimensionally was found to be very effective, achieving a reduction in peak tone magnitude of over 20 dB and a reduction in broadband SPL of up to 5 dB. In general, the results for forcing in this manner were extremely sensitive to forcing frequency. The most effective forcing frequency was found at approximately 3300 Hz. Forcing was also conducted in several three-dimensional configurations. Overall certain three-dimensional configurations were found to be more effective than the quasi-two-dimensional forcing, and significantly less sensitive to frequency.
Particle image velocimetry was used to understand how the forcing affected the shear layer. Interesting vortex dynamics such as possible vortex merging was observed, the details of which help to understand why certain frequencies are more effective than others. It was determined that the vortices in the shear layer are significantly weaker under three-dimensional forcing compared to quasi-two-dimensional forcing. This could help to explain the overall increase in effectiveness seen with three-dimensional forcing.
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