Knowledge Bank

As the prioritization of high speed, agile aircraft continues to increase, the utilization of delta wing configurations has become common practice. Delta wing aerodynamics are typically dominated by the formation of a leading-edge vortex (LEV), which is a principal flow feature of many highly swept wing configurations. The LEV forms from shear layer shedding stemming from the pressure surface of the wing, where the flow is then reattached on the suction surface. This interaction forms a vortical flow feature with a low-pressure, lift inducing core. However, at high angles of attack, this LEV bursts. Bursting indications include increased radius, decreased vorticity, and decreased axial core velocity. This study designed and tested a leading-edge row of nine active flow control (AFC) jets in efforts to extend the LEV suction peak, thus moving the bursting point outboard and increasing lift. Jet parameters were chosen based on previous studies and baseline flow visualizations. Wind tunnel testing was conducted at Re = 200,000 and varying momentum coefficient. The wing was tested at angles of attack through the entirety of the wing’s lift curve. Single jet actuation proved mostly ineffective at controlling the vortex path and increasing lift. While only slight lift increases were recorded, consistent jet effectiveness trends were seen. Following these individual jet tests, groupings of jets were formed and tested actuating simultaneously. These groupings reported significantly larger lift increases, with the three most effective configurations increasing CL max by 11.75%, 10.00%, and 9.15%. These jet groupings also recorded a 1° delay in stall compared to the baseline. Initial flow visualizations on the most effective jet combination showed minimal changes to the flow field. This indicated that rather than entraining the flow, lift enhancements were due to outboard pressure reduction in the separation region. Follow-up flow visualizations showed that for jet groupings including jet 4, the presence of a secondary vortical structure was discovered. These visualizations indicated slight flow entrainment and the ability of the jets to bend the separation line outboard, towards the leading-edge. Findings from this study proved the ability of a leading-edge row of jets to entrain flow from an LEV and increase lift. While visualizations did not show a full LEV extension, small sectors of flow were entrained by the jets. This was indicated by the presence of a secondary vortical structure downstream of jet 4. These results should be used to inform future positioning of leading-edge jets. Future work should also include a computational model to fully understand the three dimensionality of these vortical features. This study’s results, at a base level, provided a foundation of knowledge for a leading-edge row of AFC jets on a blunted leading-edge cropped delta wing, which should be refined for increased performance.