Most of nature’s creatures which can fly are equipped with flexible or deformable wings. It is widely thought that wing flexibility and wing deformation would potentially provide new aerodynamic mechanisms of aerodynamic force productions over completely rigid wings in flying. However, despite some recent quantitative visualization of insect in tethered flights, little work has been done on detailed measurements of 3D wing deformation during flapping and the associated aerodynamic benefits in the study of animal free flights. This is mainly due to the small wing size, fast motion of the wing, and unpredictability of moving direction of flying insects/birds which make it very hard to perform high-speed visual tracking of the details of wing flexions.

We aim at a quantitative understanding of wing deformation and motions of nature flyers: dragonfly, damselfly, cicada, and more in free flights (take-off, hover, cruise, and turn). Related fluid dynamics mechanisms will be investigated by collaborating with biologists, structure specialist, and experimental fluid dynamicists. The goal of this research is to advance the fundamental knowledge of biological fluid dynamics in animal flight through an integrated computational and experimental approach. Two sets of techniques composed of measurement and computational flow simulation/analysis are currently being developed to make this integration possible. The measurement tools, including data acquisition using high-speed photogrammetry technology and accurate data reconstruction, quantify the wing flexion and body kinematics of animals in free flight with extraordinary detail. The 3D computational flow simulation and analysis tools include direct numerical simulation (DNS), flow visualization through Eulerian vorticity and Lagrangian coherent structure; and instantaneous locomotive force computation via CFD methods and Lagrangian wake dynamics.

We hope this study will lead to valuable insights into enduring scientific mysteries about flow mechanisms of low speed flying in nature and in turn will benefit to the flapping-wing micro aerial vehicle (MAV) design and optimization research in the future. From biological point of view, detailed investigation of wing flexions and its induced ambient flow can allow biologists to study diverse biological processes such as odor tracking during flight, heat loss, water loss and perception of wing motion when flying in swarms in a more accurate way.