Active Control of a High Reynolds Number Mach 0.9 Axisymmetric Jet
Active control of aMach 0.9 circular jet with a Reynolds number of 7:6 10 was conducted using eight localized arc filament plasma actuators, equally spaced azimuthally just upstream of the nozzle exit. Detailed two-component particle image velocimetrymeasurements were carried out on a streamwise plane passing through the jet centerline. The forcing Strouhal number was varied from 0.09 to 3.08 at azimuthal modes m 0–3, 1, 2, and 4, the attainable modes with eight actuators. The spreading of the jet with downstream distance was used as a metric for determining the optimum forcing Strouhal number at a given azimuthal mode. For all azimuthal modes except m 3, the most effective forcing was at a Strouhal number of about 0.3, which is in agreement with the results in the literature for low-Reynolds-number and low-speed flows. For am 3 mode, the maximum spreading was achieved at a forcing Strouhal number of 0.09. For a fixed Strouhal number at about 0.3, the flappingmode (m 1) resulted in best entrainment and mixing, or jet spreading. Conditionally sampled velocity contours were used to obtain Galilean velocityfield and streamlines, whichwere used to reveal the evolution and interaction of the generated largescale structures and their roles in the jet development and spreading. The nature of jet spreading and development are explained by the dynamics of large-scale structures, including the mutually and self-induced velocity field. The convection velocity of the generated large-scale structureswas determinedusing the spatial correlation of the velocity field for various forcing Strouhal numbers and modes, which varied from approximately 0:55Uj to 0:75Uj for lower to higher forcing Strouhal numbers, respectively.