On the use of single dielectric barrier discharge plasma actuators for improving the performance of airfoils

The applicability of Single Dialectic Barrier Discharge (SDBD) plasma actuators for use as active flow control devices, capable of enhancing the performance of airfoils, was assessed in this investigation. Measurements were carried out on two thick airfoils with simple flaps, a NACA0021 and an airfoil similar to those commonly used on tilt-rotor aircraft. The chord length of the airfoils was approximately 0.3 and 0.25 meters respectively and the span was approximately 0.6 meters. They were both tested in the same wind tunnel with a test section of 0.6 meters × 1.1 meters. Free-stream velocities varying from 5 m/s to 15 m/s were tested, corresponding approximately to chord Reynolds numbers ranging between 0.8×10⁵ & 3×10⁵. The lift, moment and form drag were obtained from the pressure distributions over the airfoil's surface while the total drag was calculated from a wake survey. The range of incidence angles, α, varied from -4° < α < +20° and flap deflections, δ_f, of 0° and 15° were tested. The location of the actuation was also altered. Two data sets are presented: one where the actuator was placed at approximately 5% of the chord and the other where it was located just upstream of the flap shoulder at a chord location corresponding to about 75%. The momentum input of the SDBD plasma actuators was measured with a hot wire and was in good agreement with previously published results. The input momentum is very weak and is not sufficient to prevent separation at Reynolds numbers greater than 100,000. The SDBD plasma actuators used in this study may only provide sufficient momentum to be effective at very low Reynolds numbers, such as those appropriate to micro-air-vehicles. Under special circumstances their passive presence on the surface may trip the boundary layer making it more resistant to separation, but in those cases a proper roughness strip or vortex generators may delay separation more effectively.