Abstract
This paper reports on the visualization of the flow generated by flapping of the dragonfly, Sympetrum frequens, fixed in a uniform flow velocity 0.6 m/s with smoke wire method. Two types of flapping, smaller and larger rotational angular oscillations withh mean angle 3-5 degree and about 80 degree, respectively, were observed. For smaller flapping, regular and irregular types of a sheet of shed vortices were observed. One in the regular type showed the locking phenomenon, in which the flapping frequency agreed with that of vortices as observed in Karman vortex. For larger flapping, it was clearly observed that the uniform flow was induced toward the dragonfly and the wake led into largely disturbed region. Also, it was identified that the wake velocity was faster than that of uniform flow, and then the flow exerted forward force on the dragonfly.
