Three-dimensional vortex structure in a wake of a free-flight butterfly

Abstract

A number of studies on not only the mechanism of insect flight but also the flow field around insect wings have been performed. Especially, a number of recent studies have examined the flow field around insect wings using experimental and numerical approaches. The vortex structure and the dynamic behavior generated by the wings of insect are expected to be important for generating the aerodynamic forces required for flight. In the present study, we attempt to clarify three-dimensional vortex structure in the wake of a free-flight butterfly from the viewpoint of the velocity fields. We conducted two kinds of PIV measurements, such as a stereo PIV and a scanning PIV, in the wake of a free-flight butterfly (Idea leuconoe) and visualized a three-dimensional vortex structure in the wake. The three-component velocity vectors formed in the wake of a free-flight butterfly were obtained by stereo PIV measurements. Jets induced by the vortex rings in the wake were visualized clearly and a three-dimensional vortex structure in the wake was expected by the dynamic behaviors of jets. The formation of an L-shaped wake structure due to an interaction of the vortex rings produced during upward and downward flapping was obtained by scanning PIV measurement. On the basis of these results, the vortex rings produced during upward and downward flapping were formed continuously in the wake of the free-flight butterfly and they became the formation of an L-shaped wake structure.

Keywords

• vortex
• wing
• wake
• visualization
• piv meseurement