Parameters Governing Separation Control with Sweeping Jet Actuators

Parameters governing separation control by sweeping jet actuators are investigated experimentally on a generic “Multiple Flap Airfoil” (MFA). Neither the flow rate nor the momentum input is found to be a sole parameter governing the lift for varying distance between adjacent actuators. However, the product of the mass flow coefficient and a square root of the momentum coefficient collapses the lift onto a single curve regardless of the actuator spacing. Surface flow visualization on the flap suggests the formation of counterrotating pairs of streamwise vortices caused by the interaction of neighboring jets. The actuation intensity required to attach the flow increases with increasing distance from the flap shoulder and increasing flap deflection. No obvious dependence of the ideal actuation location on flap deflection, angle of attack, or actuation intensity is found within the tested range. Comparisons between experimental and numerical results reveal a strong dependence on the thickness of the last flap segment at its hinge. In absence of this geometrical effect potential flow solution appears to be a suitable predictor for the obtainable lift. The flap size affects the achievable lift, the accompanying drag, the required flap deflection, and actuation intensity. By controlling separation the range of achievable lift coefficients is doubled without significant penalty in drag even when considering a safety margin for the maximum applicable incidence.