Interactions of an Array of Finite Span Synthetic Jets and a Crossflow

The formation of secondary flow structures due to the interaction of an array of three finite span synthetic jets with a crossflow was investigated experimentally over a finite swept-back wing (NACA 4421, AR = 4, sweep angle of 30 deg, Reynolds number of 1 x 10(5)). Stereoscopic particle image velocimetry data were collected in the midspan section of the wing, where the effects of the jets' combinations and their blowing ratios were analyzed based on the three-dimensional flowfield using time-and phase-averaged statistics. The focus of the present work was to capture the formation and advection of secondary flow structures in the vicinity of the synthetic jets for different combinations of jets, including 1) only the center jet activated, 2) two synthetic jets off the middle jet activated, and 3) all three synthetic jets actuated. An angle of attack of 13.5 deg was selected, in which the boundary layer was either attached (in the vicinity of the middle jet) or partially separated (in the vicinity of the jet closer to the wing tip). The time-averaged total velocity fields exhibited secondary streamwise structures that were formed along the jets orifice span. Furthermore, the effect of the synthetic jet(s) was felt at spanwise locations (toward the wing tip) away from the point of activation. From the phase-averaged flowfield, it was shown that, during the blowing portion of the synthetic jet cycle, quasi-two-dimensional pairs of counter-rotating spanwise rollers were formed at the jet exit plane. Each pair was advected downstream as time progressed, bent and tilted toward the tip, and eventually broke down into smaller structures farther downstream, which resulted in the formation of secondary streamwise structures.