Leading-edge Vortices Over Swept-back Wings*

Micro air vehicles are used in a myriad of applications, such as transportation and surveying. Their performance can be improved through study of new wing designs and lift generation techniques including leading-edge vortices (LEVs). Observation of natural fliers, e.g., birds and bats, has shown that LEVs are a major contributor to lift during flapping flight, and the common swift (Apus apus) has been observed to generate LEVs during gliding flight. Particle image velocimetry experiments were performed in a water flume to measure flow over wings with non-linear sweep (swift-like wing), linear sweep (delta wing), and zero sweep (rectangular wing). Experiments were performed at three spanwise planes at four angles of attack for a chord-based Reynolds number of 25280. Streamlines, vorticity, swirling strength, and Q criterion, were used to identify LEVs for each experiment. The results show that LEVs exist at attack angles of 20° and 30° for both the delta and swift wing geometries and that the vortex evolution along the wing span is similar for the two wing geometries. The similar vortex structure over both wings suggests that multiple swept leading-edge geometries are capable of creating similar LEVs.