Active Control of a High Reynolds Number Mach 0.9 Axisymmetric Jet

Active control of a Mach 0.9 circular jet with a Reynolds number of 7.6 x 10(5) was conducted using eight localized arc filament plasma actuators, equally spaced azimuthally just upstream of the nozzle exit. Detailed two-component particle image velocimetry measurements 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 in = 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 in = 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 a in = 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 flapping mode (m = +/-1) resulted in best entrainment and mixing, or jet spreading. Conditionally sampled velocity contours were used to obtain Galilean velocity field and streamlines, which were used to reveal the evolution and interaction of the generated large-scale 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 structures was determined using the spatial correlation of the velocity field for various forcing Strouhal numbers and modes, which varied from approximately 0.55U(j) to 0.75U(j) for lower to higher forcing Strouhal numbers, respectively.