Disappearance of Vortex Lift in Low-Aspect-Ratio Wings at Very-low Reynolds Numbers

The objective of this study is to ascertain the aerodynamic characteristics of low-aspect-ratio wings at Reynolds numbers ranging between 1×103 and 1×104 which correspond to insect wings. The wings tested in this study are rectangular, thin, flat plates with aspect ratios varying from 0.5 to 2. The very small forces and moment acting on the wings were measured using a low-pressure wind tunnel. Although a large maximum lift coefficient was obtained for the wing with an aspect ratio of 1 at a Reynolds number of 1×104, it decreased as the Reynolds number decreased due to the disappearance of vortex lift. That is, the Reynolds number effects of low-aspect-ratio wings were found at the current Reynolds number. However, as the aspect ratio of the wing changed, the rate at which the maximum lift coefficient decreased was reduced. The main cause of the phenomenon was the behavior of the wing-tip vortices. These aerodynamic characteristics of wings will be important for developing insect-sized aircraft.