Active control of high-speed and high-Reynolds-number jets using plasma actuators

Localized arc filament plasma actuators are used to control an axisymmetric Mach 1.3 ideally expanded jet of 2.54cm exit diameter and a Reynolds number based on the nozzle exit diameter of about 1.1 X 10(6). Measurements of growth and decay of perturbations seeded in the flow by the actuators, laser-based planar flow visualizations, and particle imaging velocimetry measurements are used to evaluate the effects of control. Eight actuators distributed azimuthally inside the nozzle, approximately 1 mm upstream of the nozzle exit, are used to force various azimuthal modes over a large frequency range (St(DF) of 0.13 to 1.3). The jet responded to the forcing over the entire range of frequencies, but the response was optimum (in terms of the development of large coherent structures and mixing enhancement) around the jet preferred Strouhal number of 0.33 (f = 5 kHz), in good agreement with the results in the literature for low-speed and low-Reynolds-number jets. The jet (with a thin boundary layer, D/theta similar to 250) also responded to forcing with various azimuthal modes (m = 0 to 3 and m = +/- 1, +/- 2, +/- 4), again in agreement with instability analysis and experimental result;; in the literature for low-speed and low-Reynolds-number jets. Forcing the jet with the azimuthal mode m = +/- 1 at the jet preferred-mode frequency provided the maximum mixing enhancement, with a significant reduction in the jet potential core length and a significant increase in the jet centreline velocity decay rate beyond the end of the potential core.