High-Speed Schlieren Imaging as a Tool for Identifying Vortices in Dragonfly Flight

Bio-inspired aerodynamics has amazed the scientific community for decades now. It has inspired researchers and innovators to identify solutions to several fundamental and advanced problems in academia and industry. Insight into temporally evolving vortical structures developing in the near field of a beating wing will be helpful to interpret better the aerodynamic forces generated by the flap cycle of an insect. In the present study, high-speed Schlieren imaging is implemented to capture vortex structures on the wings of Pantala flavescens in the tethered arrangement. The method discussed here helps identify various vortical structures like leading edge vortex and trailing edge vortex. A physics-based optical flow method is also implemented to quantify the flow field and interpret the jump in the nature of vorticity during wing rotation at the end of the stroke. It is also demonstrated that this method has the potential to capture the vortex structure. The present study illustrates how this method is not limited to presenting flow visualization or qualitatively complementing the force measurement tests but also has the potential to provide a quantified velocity field.