Meeting Abstract
Tiny flying insects of body lengths under 2 mm, such as thrips and fairyflies, possess bristled wings and use wing-wing interaction via the ‘clap and fling’ mechanism to augment lift generation at chord-based Reynolds number (Re) on the orders of 1-10. When compared to solid wings, bristled wings have been shown to decrease drag required to fling wings apart. We used a dynamically scaled robotic platform fitted with physical bristled wing models to examine the aerodynamic importance of initial inter-wing spacing of bristled wings during fling. Three sets of motion profiles were considered: 1) wings purely rotating about their trailing edges; 2) pure translation of each wing at a fixed angle of attack (AOA); and 3) overlapping rotation and translation of each wing, all at Re=10. The results show that (i) average drag coefficient increased during pure rotation and pure translation with increasing AOA (relative to horizontal), (ii) decreasing initial inter-wing spacing increased the lift coefficient due to formation of weaker trailing edge vortices, resulting in asymmetric leading and trailing edge vortices. Previous studies have shown leakiness of flow through bristles to aid in decreasing drag. However, we found that both peak drag and leakiness increased with decreasing initial inter-wing spacing during pure rotation. We observed large negative pressure distribution along the chordwise direction within the cavity between the two wings, which we suspect causes fluid to leak through the bristles. This suggests that increasing leakiness does not necessarily decrease drag during pure rotation in early fling. The contribution of leakiness to pressure and viscous drag reduction will be presented.
