Characteristics of Dynamic Forces Generated by a Flapping Butterfly Wing Related with the Dynamic Behavior of the Vortex Rings

The flow field around the butterfly wing is one of the most common unsteady flows around the moving elastic body. Because the butterflies fly by skillfully controlling their wings, which deform elastically, and vortices are generated around their bodies. The elastic wing motion of the flying butterflies produces a dynamic fluid force by manipulating the flow field around wing. Recently, the complex flow structures around the flapping insect wings have been visualized clearly using quantitative flow visualization techniques. The authors visualized the dynamic behavior of vortex rings that forms over the tethered flapping insect wings, Cynthia cardui and Idea leuconoe, using two-dimensional PIV. Moreover, the authors visualized a three-dimensional vortex structure in the wake of free-flight Cynthia cardui and Idea leuconoe using scanning PIV. Furthermore, the authors directly measured the dynamic lift of tethered flapping butterflies using a six-axes sensor. However, the characteristic of the dynamic forces generated by the flapping butterfly have not been understood sufficiently. The purpose of the present study is to understand quantitatively the characteristics of dynamic forces generated by the flapping butterfly wing related with the dynamic behavior of the vortex ring by the dynamic force measurement using six-axes sensor and the PIV measurements.