Tests on in-flight drag reduction using AC-DBD plasma flow control

Dielectric Barrier Discharge (DBD) plasma actuators have demonstrated significant potential for active flow control, owing to their distinct advantages, including the absence of moving mechanical parts, a lightweight structure, and rapid response time. 24 pairs of alternating current DBD plasma actuators were arranged on a Davis wing. The flow control effectiveness and drag-reduction performance were systematically evaluated through wind-tunnel force measurements, Particle Image Velocimetry (PIV) flow-field measurements, and actual flight tests. Wind tunnel results indicate that plasma actuation effectively modulates near-wall flow structures. The wall jet induced by the actuation interacts with near-wall structures, leading to changes in coherent structures: compression of the streamwise extent, enlargement of the spanwise streak spacing, and a reduction in the inclination angle from 15.94° to 9.20°. This flow-control effect suppresses the lift-up motion of quasi-streamwise vortex pairs, weakening momentum transport and attenuating Reynolds shear stress in the near-wall region, thereby reducing skin-friction drag. Based on these findings, circling flight tests were conducted using an unmanned aerial vehicle at a fixed altitude and airspeed. Drag reduction effects were evaluated by monitoring changes in motor power under conditions of an airspeed of 24 m/s, a peak-to-peak actuation voltage of 10 kV, and an angle of attack of 4° (close to the maximum lift-to-drag ratio state). The results demonstrate that upon activating plasma actuation, the aircraft's ground speed increased by approximately 7.1%, with a peak drag reduction of 7.59% and an average drag reduction of 6.15%. The consistent drag-reduction trends observed in both wind tunnel and flight tests validate the effectiveness and engineering feasibility of this flow-control method in real-world flight environments.