Hybrid Control of a Turret Wake, Part I: Aerodynamic Effects

Effects of active and hybrid flow control on the aerodynamic characteristics of flow over a 0.254 m diameter conformal optical aperture embedded in the hemispherical cap of a cylinder turret model (D = 0.61 m) are investigated at M = 0.3 – 0.5 and ReD = 4.4–7.4·10. Resulting mean flows are characterized by surface static pressure distributions and oil-flow visualizations, while the separated flow dynamics is assessed by hot-film measurements. Active flow control is effected by arrays of piezoelectrically-driven synthetic jet modules distributed in multiple arrays upstream from the aperture. Active flow control is further assisted by global flow alterations induced by a passive forward partition plate, and, when combined, constitute hybrid flow control. It is shown that the hybrid flow control combines the positive effects of its component control elements to yield superior results in any cumulative aerodynamic aspect of the separated flow. This cumulative effect of the actuation is manifested by concomitant delay of flow separation and active, dissipative suppression of turbulent motions downstream of separation. It is also demonstrated by means of direct 2D wavefront measurements that the overall aerodynamic improvements correlate with substantial suppression of optical aberrations through the separated flow. Furthermore, estimated Strehl ratios for the laser beam indicate that nearly-invariant Strehl ratio is established within the range of tested aperture elevation angles, yielding improvement of about 50% for the highest elevation angle.