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A supersonic axisymmetric jet of design Mach number 1.3 operated in perfectly- and imperfectly-expanded flow regimes is excited by using localized arc filament plasma actuators (LAFPAs). The jet is operated at three fully-expanded jet Mach numbers (MJ) of 1.2 (over-expanded), 1.3 (perfectly-expanded), and 1.4 (under-expanded). The Reynolds number based on the jet diameter and jet exit velocity ranges from 1.1×106 to 1.4×106. Eight equally-spaced LAFPAs are housed in a boron nitride nozzle extension. The forcing Strouhal number is ranged from 0.07 to 2.62 for azimuthal modes of 0-3, ±1, ±2, and ±4. In the perfectly-expanded jet, the most effective forcing is obtained at m = ±1 and the jet spreading is significantly enhanced at a forcing Strouhal number of about 0.3 at this mode. For the perfectly-expanded jet, the effects of forcing on the jet development and structure formation are very similar to those observed in a MJ = 0.9 subsonic jet, which has been investigated previously. However, the generated structures in the imperfectly-expanded jets are less energetic due to the competition for energy between the perturbations seeded by the actuators and naturally existing perturbations amplified by the flow and acoustic feedback loop. As a result of this phenomenon, in addition to the fact that the jet mixing is already enhanced by the feedback loop, the mixing enhancement due to the control in the imperfectly-expanded jets is less significant.

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