Taichi Kuroki

Three-Dimensional Vortex Structure Around a Free Flight Butterfly

Micro-air-vehicles (MAVs) and micro-flight robots that mimic the flight mechanisms of insects have attracted significant attention. From this reason, the flight mechanism of the butterflies and their flow fields also has attracted attention. A number of studies on the mechanism of butterfly flight have been carried out. Moreover, a number of recent studies have examined the flow field around insect wings. The present authors conducted a particle image velocimetry (PIV) measurement around the flapping wings of Cynthia cardui and Idea leuconoe and investigated the vortex structure and dynamic behavior produced. However, these results are for a flow field under a fixed condition. The vortex flow structure and the dynamic behavior generated by the wings of a butterfly in free flight are expected to be important for generating the aerodynamic forces required for flight. In the present study, we attempt to clarify the three-dimensional vortex structure around a butterfly in free flight by a scanning PIV measurement. The vortex ring formed by the front wings during the flapping downward grows without attenuation toward the wake. Moreover, during the flapping upward of the wings, a vortex rolls up from the wing, eventually forming a single vortex ring. This vortex ring forms in the vertical direction in contrast to vortex ring formed during the flapping downward, and we may anticipate that the two vortex rings interfere with each other as they advance toward the wake.Copyright

Characteristics of Dynamic Forces Generated by a Flapping Butterfly

Many studies on the mechanism of butterfly flight have been carried out. A number of recent studies have examined the flow field around insect wings. Moreover, Micro-air-vehicles and micro-flight robots that mimic the flight mechanisms of insects have attracted significant attention, and a number of MAVs and micro-flight robots that use various devices have been reported. However, these robots were not practical. One of the reasons for this is that the flying mechanism of insects has not yet been clarified sufficiently. The present authors developed a flapping-wing robot without tail wings and focused on the flow field around the wings created by the flapping motion and its elastic deformation. In the present study, we attempt to clarify the relationship between the vortex ring over the wing and the dynamic lift generated by the flapping wing. The dynamic lift becomes large rapidly in the downward flapping and reaches a maximum at a flapping angle of −30 deg. After the maximum, the dynamic lift decreases gradually and the dynamic lift in upward flapping is approximately constant. The growth of the vortex ring formed by the flapping wing was clarified to contribute significantly to the dynamic lift acting on the butterfly. We should consider the interaction of both vortex ring both in downward flapping and in upward flapping in order to estimate the dynamic lift exactly using the circulation of the vortex ring.Copyright

Dynamic Behavior of a Vortex Ring over a Butterfly Wing and Its Dynamic Lift

Recently, the mechanism of butterfly flight has attracted significant attentions in biohydrodynamics. Especially, a number of recent studies have examined the flow field around an insect wing. However, the detailed flow structure around insect wing and its growth process have not been understood. The purpose of the present study is to clarify the dynamic behavior of the vortices around the flapping butterfly wing. Moreover, we estimated the dynamic lift produced by the butterfly wing using the circulation of the vortex ring. A vortex ring is formed over the butterfly wings when the wings flap downward to the bottom dead position, and then passes through the butterfly completely and grows until reaching the wake at the bottom dead position. The dynamic lift produced by the butterfly wing in flapping downward estimated using the circulation of the vortex ring. The dynamic lift becomes large rapidly as the vortex ring develops over the wing sufficiently. Maximum lift is about four times of the gravity of the butterfly at -30 deg.

Dynamic Behaviors of a Vortex Ring on a Butterfly and a Small Flapping Robot

Butterflies fly combining wing flapping and gliding efficiently and have beautiful flight patterns. Micro-Air-Vehicles (MAVs) and micro-flight robots that mimic the flight mechanisms of insects have been attracting significant attention in recent years. A number of MAVs and micro-flight robots that use various devices have been reported. However, these robots were not practical. A number of studies on the mechanism of butterfly flight have been carried out. Moreover, a number of recent studies have examined the flow field around an insect wing, such as a leading edge vortex (LEV) structure using the first digital particle image velocimetry (DPIV). We have carried out the PIV measurement around a butterfly wing and have visualized a vortex ring formed on the wing clearly. On the other hand, we developed a small flapping robot without tail wings, which is similar to the butterfly. The purpose of the present study is to clarify the dynamic behaviors of the vortex rings formed on the wings of the butterfly and the small flapping robot. A vortex ring is formed over the wings of the butterfly and small flapping robot with stable flight when the wings flap downward. An another vortex ring is formed below the butterfly wings when the wings flap upward and it was smaller than that in downward flapping motion because of the elastic deformation of the wings. Both vortex rings pass through the butterfly completely at the top and bottom dead position in the flapping motion.

Vortex Structure of a Vortex Ring Over a Butterfly Wing and its Dynamic Behavior

Micro-Air-Vehicles (MAVs) that mimic the flight mechanisms of insects have been attracting significant attention in recent years. These technologies are developed with the aim of lifesavings in the area with the risk of secondary disasters, maintenance works for constructions such as bridges, information collection on planet searches, monitoring of security risks for the purpose of security means. A number of researchers have attempted to develop small flap flying objects and MAV with various actuators and devices. However, these robots were not practical. One of the reasons for this is that the flying mechanism of insects has not yet been clarified sufficiently. We have clarified that a couple of large-scale vortex is formed over the wing. The purpose of the present study is to clarify the dynamic behavior and the detailed structure of the vortices of the flapping butterfly wing, and we carried out the PIV measurement around the flapping butterfly wing. The vortex ring develops over the wings when the wings flap downward to the bottom dead position and then passes through the butterfly completely and grows until reaching the wake at the bottom dead position. The vortex ring develops over the wing while growing from the leading edge toward the trailing edge. The maximum vorticity of the vortex ring over the wing moves from the leading edge to the trailing edge with the downward flapping. On the other hand, the vorticity of the LEV decays with downward flapping.Copyright