Characterization of a High-Lift, Supercritical Airfoil with Microjets

Active flow control (AFC) has the potential for substantial performance gains and meeting the challenges of next-generation high-lift aircraft. High-lift wings employ multi-element trailing edge flaps during takeoff and landing. When the aircraft is at cruise speed, these flaps are not required and are retracted to reduce drag. These aircraft wings with high-lift mechanisms enhance the lift characteristics at slower speeds, but suffer due to the added weight of these deployment/retraction mechanisms. In the present study, we have investigated the effect of active flow control using microjets to enhance the performance of a two-dimensional high-lift supercritical airfoil with a simply hinged flap. The airfoil used in the study is the NASA Energy Efficient Transport (EET) and the wind-tunnel tests were conducted at a freestream velocity of 20 m/s. Two different scaled models were used corresponding to Reynolds numbers of 1.3 x 105 and 3.4 x 105. The experiments pertaining to the small scaled model were carried out with two angles of incidence of 0° and 4° at a constant flap deflection of 20°. For the large scale model, a constant angle of incidence of 0° and flap deflection angles of 20° and 30° were investigated. A range of microjet momentum ratios and microjet orientations were studied for both models. Particle Image Velocimetry was carried out to study the mean velocity field and the effect of microjet control at the flap region of the airfoil. For the first model, the baseline flow at both the angles of incidence separates at the hinge line and remain separated over the entire flap region. The size of the re-circulation region is found to gradually decrease with an increase in microjet momentum ratio. Microjets oriented normal to the airfoil surface were relatively more effective and successful in re-attaching the flow over the entire airfoil at both the angles of incidence. Experiments for the second model consisted of both Planar and Stereoscopic Particle Image Velocimetry. The baseline flow is separated over a third of the flap at 20° and over the entire flap at 30°. Microjets oriented at a more tangential angle are able to completely re-attach the flow at both flap angles. In general, active flow control using high-momentum microjets was very effective in eliminating/reducing flow separation, however, its effectiveness was dependent on the geometric and flow parameters.