Single Dielectric Barrier Discharge Plasma Actuators for Improved Airfoil Performance

The applicability of single dialectic barrier discharge 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 that is similar to those commonly used on tiltrotor aircraft. The chord length of the airfoils was approximately 0.3 and 0.25 m, respectively, and the span was approximately 0.6 m. They were both tested in the same wind tunnel with a test section of 0.6 x 1.1 m. Freestream velocities varying from 5 to 15 m/s were tested, corresponding to chord Reynolds numbers ranging between 0.8 x 10(5) and 3 x 10(5). The lift, moment, and form drag were obtained from the pressure distributions over the airfoil's surface, and the total drag was calculated from a wake survey. The range of incidence angles alpha varied from -4deg < alpha < +20deg and flap deflections delta(f) of 0 and 15 deg were tested. The location of the actuation was also altered. Two data sets are presented: one in which the actuator was placed at approximately 5% of the chord and the other in which it was located just upstream of the flap shoulder at a chord location corresponding to about 75%. The momentum input of the single dialectic barrier discharge 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 single dialectic barrier discharge 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 resist-ant to separation, but in those cases, a proper roughness strip or vortex generators may delay separation more effectively.