Numerical investigation for influence of synthetic jet actuation location on airfoil flow separation control at large attack angle

For a NACA0015 airfoil, 2-D unsteady flow fields are calculated when a synthetic jet is put at different locations on the suction surface at a large attack angle (α=20°) and Reynolds number of 8.96×10⁵ based on chord length. POD (proper orthogonal decomposition) method is utilized to analyze the computation results, and relevant control mechanisms are explained. The results show that actuation location of a synthetic jet exerts significant influence on effects of flow separation control. When the actuator is located between 0.12 and 0.40 of chord length, flow separation on the airfoil is effectively suppressed, enhancing lift coefficient and reducing drag coefficient with lift to drag ratio increasing by 293%. The optimal location is not near the time-averaged separation point as widely suggested but at some downstream locations inside the separation zone. POD analysis on computation results indicates that the introduction of synthetic jets would change the energy distribution among different modes, and that energy is transferred from 1st-order mode representing mean flow to 2nd-order mode or higher modes which represent large scale coherent structures. The best location for synthetic jet actuation is closely related to the site of a characteristic vortex on the suction side of the airfoil in 2nd-order mode. In order to reach optimal control effects, synthetic actuation should be located within the covering range of the characteristic vortex. It is ineffective to put a synthetic jet at downstream or far upstream of the location of that vortex.