Flow Visualization of Micro Air Vehicle Scaled Insect-Based Flapping Wings

摘要

A flow-visualization experiment was conducted on an insect-based flapping-wing mechanism. This enabled greater understanding and insight to be gained on the unsteady aerodynamic phenomena that are responsible for the enhanced lift of wings operating at low Reynolds numbers in hovering flapping flight. Flow-visualization images were acquired with a strobbed laser sheet to illuminate the flow, which was seeded with a mineral oil fog. The general flowfield structure was found to consist of a folded wake, with a relatively large starting vortex at the end of each half-stroke. A large flow recirculation region was generated in the plane of flapping, which was centered around the two extreme flapping displacements. These general flowfleld features were enhanced by detailed observations of the local flowfield around the wing section. One observation was the presence of multiple vortices on the top surface of the wing as it underwent translation. Furthermore, the local flowfield images clearly showed the growth of the leading-edge vortex as a function of span and identified the presence of separated flow on the outboard regions of the wing. These experimental results were supported by a free vortex modeling of the wake developments. The model was found to predict similar wake flowfield dynamics to that found in the experiments. This research has contributed to a better understanding of the unsteady aerodynamic mechanisms that are responsible for the enhanced lift of insect-based flapping wings in hover.