Flow Physics of Bioinspired Wingtips for Drag Reduction

Flight mission demands for small-scale uncrewed aerial vehicles (UAVs) are increasing and require high levels of aerodynamic efficiency and maneuverability. However, current UAVs are considered point designs, meaning they are designed for only a single mission or specific flight conditions. In contrast, birds like Harris’s hawks are capable of both agile and efficient flight under various conditions, partly due to their wing morphology. For example, Harris’s hawks have moderate aspect ratio wings that enhance maneuverability but are often associated with reduced aerodynamic efficiency due to increased induced drag. However, their wing tip slots have been shown to spread vorticity both horizontally and vertically, a mechanism hypothesized to reduce induced drag. In this study, we examine the design of a biologically relevant wing with various Harris hawk-inspired wingtip configurations to study the effect of wing tip slots on aerodynamic performance. Experiments are conducted in the 4’x4’ wind tunnel facility at Princeton University at Re = 2 x 10⁵. Time-resolved forces and flow field measurements will be used to understand how wingtips improve aerodynamic performance by altering the vortex structures in the flow. Such an understanding can enable a new generation of UAVs capable of a broad range of missions that require both agility and efficiency.