トンボの羽ばたきにより生じる流れ

概要

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When a dragonfly (Pantala flavescens) on a stem in a wind tunnel was flapping in a flapping angle of 3～5° in a head wind with velocity of 1.14 m/s, flows which occurred by flapping were observed using smoke wire method. The flows passed through a forewing at the distance of about 32mm from the root of the forewing and a hind wing. Reynolds number was about 498 (based on a chord length of the forewing). The flapping frequency was 40～50Hz, the amplitude of 3～4mm and the phase difference of flappings between the fore- and hind wings of about 180° by observation of a high-speed video camera. Also, the configuration of the wings of the dragonfly was flexibly changing during the flapping. A street of vortices with two centers or various types of vortex according to the flapping state were observed downstream of the trailing edge of the hind wing. Moreover, the process of formation of each vortex in the street of vortices with two centers was clarified with time sequence. The ratio of vertical distance to horizontal one between each vortex in the street of vortices with two centers was about 0.31.