A plasma actuator comprising a dielectric layer sandwiched between upper and lower\nelectrodes can induce a flow from the upper to lower electrode by means of an externally-applied\nelectric field. Our objective is to clarify the mechanism by which such actuators can control the cavity\ntone. Plasma actuators, with the electrodes elongated in the streamwise direction and aligned in the\nspanwise direction, were placed in the incoming boundary of a deep cavity with a depth-to-length\nratio of 2.5. By using this experimental arrangement, the amount of sound reduction (ââ?¬Å?control effectââ?¬Â)\nproduced by actuators of differing dimensions was measured. Direct aeroacoustic simulations\nwere performed for controlling the cavity tone by using these actuators, where the distributions\nof the body forces applied by the actuators were determined from measurements of the plasma\nluminescence. The predicted control effects on the flow and sound fields were found to agree\nwell with the experimental results. The simulations show that longitudinal streamwise vortices\nare introduced in the incoming boundary by the actuators, and the vortices form rib structures in\nthe cavity flow. These vortices distort and weaken the two-dimensional vortices responsible for\nproducing the cavity tone, causing the tonal sound to be reduced.
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