Leading-edge vortices over swept-back wings with varying sweep geometries

• Published in: Royal Society Open Science
• Main Authors: Lambert, William B., Stanek, Mathew J., Gurka, Roi, Hackett, Erin E.
• Other Authors: National Science Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2019
• Subjects: Apus apus
• Online Access: http://dx.doi.org/10.1098/rsos.190514; https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.190514; https://royalsocietypublishing.org/doi/full-xml/10.1098/rsos.190514

Micro air vehicles are used in a myriad of applications, such as transportation and surveying. Their performance can be improved through the study of 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. We hypothesize that nonlinear swept-back wings generate a vortex in the leading-edge region, which can augment the lift in a similar manner to linear swept-back wings (i.e. delta wing) during gliding flight. Particle image velocimetry experiments were performed in a water flume to compare flow over two wing geometries: one with a nonlinear sweep (swift-like wing) and one with a linear sweep (delta wing). Experiments were performed at three spanwise planes and three angles of attack at a chord-based Reynolds number of 26 000. Streamlines, vorticity, swirling strength, and Q -criterion were used to identify LEVs. The results show similar LEV characteristics for delta and swift-like wing geometries. These similarities suggest that sweep geometries other than a linear sweep (i.e. delta wing) are capable of creating LEVs during gliding flight.