FLOW over the sharp leading edges of a delta wing at high angles of attack separates and forms shear layers that roll up into two large vortices, which are primarily responsible for lift generation at low speeds. These vortices are only weakly dependent on Reynolds number when the leading edge is sharp [1]. As the angle of attack increases, the swirl velocity of the vortices also increases. When the ratio of swirling velocity to axial velocity at any point in the vortex exceeds approximately 1.3, the vortex breaks down; that is, it expands into a highly fluctuating structure in which the velocity components are drastically reduced in the central part of the structure [1]. Consequently, vortex breakdown is generally associated with delta-wing stall and can induce vibrations resulting in tail buffet, loss of control, and possible wing damage. A number of investigators have suggested that shear-layer instabilities are linked with both the development of leading-edge vortices and their breakdown [2, 3]. Vortices that have undergone breakdown can be viewed as curved shear layers, and perturbations introduced along the leading edge profoundly affect them, producing significant changes to the wing’s normal force [4]. The underlying mechanism of performance enhancement by periodic excitation on a delta wing is unclear, with speculations ranging from delay of vortex breakdown to vortex enhancement. It was suggested in [5] that vortex breakdown could be delayed by about 25% of the chord by introducing periodic perturbations at the leading edge. In contrast, water-tunnel particle image velocimetry (PIV) data [6] suggest that the vortex-breakdown location is not altered, but that the downstream directed velocity close to the surface is increased, thereby decreasing the upper-surface pressure. A follow-up study [7] ascertained that excitation from the aft half of the leading edge in the vicinity of the vortex-breakdown location was most effective. PIV measurements revealed that the shear layer transports high streamwise momentum fluid into the wake, downstream of the breakdown location. The most detailed study appears to be that of [4], in which cavity-installed piezoelectric actuators were employed to effect control. Optimum performance was achieved when the high resonance frequency was burst-modulated to produce F O 1, with duty cycles (DCs) around 5%. Two-dimensional PIV measurements suggested that excitation enhances the momentum transfer across the shear layer, downstream of the original vortexbreakdown location, generating a streamwise vortex for which the size is commensurate with the local wingspan. For delta wings or swept planforms with a low aspect ratio and at low Reynolds numbers [typical of some micro air vehicles (MAVs)], leading-edge vortices also serve as a dominant mechanism of lift generation. It therefore stands to reason that periodic excitation may be effective for enhancing MAV performance or controlling flight. However, on vehicles of this size (typically, 15 cm), it may be impractical to install zero-mass-flux actuators within the vehicle structure or to attach oscillators to the surface. In these instances, dielectric barrier discharge (DBD) actuators [8, 9] emerge as a strong candidate for leading-edge vortex control. Previous work by some of the authors of this Note [10–12] demonstrated the effectiveness of such actuators on airfoils at Re< 100; 000 (or U1< 10 m= s), consistent with typical MAV Reynolds numbers. The present limited investigation addressed two specific objectives. The primary objective was to maximize delta-wing performance at low speeds (Re 75; 000) using leading-edge DBD

Presented as Paper 4277 at the 25th AIAA …