Low-dimensional Modeling and Aerodynamics of Flexible Wings in Flapping Flight

All natural flyers equip flexible wings. It’s widely thought that the wing flexibility can play important roles in flight aerodynamics. In the current work, a combined experimental and computational method is developed to study the role of morphing wing in hovering dragonfly aerodynamic performance. We start with taking high-speed images of a freely flying dragonfly. Next, a surface reconstruction method is used to obtain detailed kinematical and morphological data from the raw high-speed images. After that, spherical-coordinates-based singular value decomposition (SSVD) is applied to decompose the morphing wing kinematics into simple modes. Results have shown that the first two SSVD modes contain 93.1% of the hovering wing motion. The mode 1 (flapping mode) consists of a simple flapping motion, and the mode 2 (morphing mode) contains dynamic wing morphing in both span-wise and chord-wise directions. By evaluating the aerodynamic role of the SSVD modes using a high-fidelity flow simulation, we further conclude that the first two modes can recover more than 96% of the lift production and 91% of the lift economy comparing to the original flapping wing aerodynamcis whereas the mode 1 only produces 5% of the lift and 4% of the lift economy. The associated flow mechanisms of the morphing mode are found to be the reduced wing tip vortex and the improved attachment of leading-edge vortex.