蝶の翅の羽ばたき運動により生成される渦輪と非定常揚力

抄録

Elastic moving body have attracted many researchers because the elastic moving body is superior to rigid moving body. Flapping motion of butterfly wing is one of the examples of elastic moving airfoil. Vortex ring is the evidence for fluid force generated by moving body. However, it is not easy to grasp the entire structure of vortex ring and estimate fluid force from vortex ring. In this study, we clarified not only the dynamic behavior of a pair of vortex rings but also the dynamic lift generated by flapping motion of butterfly wing. We implemented the 2DPIV to the flow field around butterfly wing from only two directions in order to cut off the quantity of information. From the visualization results, we predicted the dynamic behavior of vortex rings. It found that the vortex ring generated by upstroke is interfered by the induced flow of vortex ring generated by downstroke. That interference is resulted in the disturbance of developing and moving upward of vortex ring’s rear part generated by upstroke. From prediction result of vortex rings, we proposed the change and amplitude of dynamic lift generated by each stroke. Eventually, the dynamic lift tendency is matched with not only the estimation results but also direct measurement result. From that, we could predict the dynamic lift from the dynamic behavior of vortex rings. In addition, it found that upstroke of the butterfly wing hardly contributes the generation of dynamic lift because dynamic lift is negative and small on upstroke.