Improvement of Poststall Performance of NACA 0015 Airfoil Using Leading-Edge Synthetic Jet Array

Wind tunnel experiments were conducted to explore the control effect of a synthetic jet actuator array placed at the leading edge of a National Advisory Committee for Aeronautics (NACA) 0015 airfoil at two Reynolds numbers of 1.1x105 and 1.6x105. Synthetic jets were generated perpendicular to the leading edge with high-frequency excitation to imitate the biomimetic effect of leading-edge tubercles. Force measurements over the angle of attack alpha from 0 degrees to 40 degrees display similar aerodynamic characteristics between the present synthetic-jet-controlled airfoils and previous leading-edge tubercled ones in both the prestall and poststall regimes. Thus, virtual tubercles constructed by synthetic jets can be used to effectively improve poststall aerodynamic performance of airfoils. Flow field characteristics at alpha=8 degrees, 16 degrees, and 32 degrees were analyzed to reveal the control mechanism at different angles of attack. At alpha=8 degrees, synthetic jets ruin the high-velocity flow region on the suction surface, resulting in attenuated aerodynamic performance in the prestall regime. In the poststall regimes, however, synthetic jets can directly inject high momentum into the separated shear layer at alpha=16 degrees, which energizes the boundary layer and thus delays flow separation. As alpha increases to 32 degrees, synthetic jets can still improve the lift performance to some extent by enhancing momentum exchange between the outer high-velocity flow and inner low-velocity separation region. In particular, synthetic-jet tubercles can provide the potential for better practicality and higher efficiency than traditional leading-edge tubercles in improving unsteady aerodynamic characteristics.