Clap and fling with bristled wings: effects of varying inter-bristle spacing

The smallest flying insects with body lengths under 1 mm, such as thrips and some parasitoid wasps, show the following morphological and kinematics adaptations: 1) wings consisting of a thin membrane with long bristles at the fringes; and 2) obligatory use of wing-wing interaction via clap and fling for flapping flight at Reynolds numbers (Re) on the order of 1 to 10. Previous studies have shown that bristles can lower lift and drag forces generated during clap and fling. However, flow through the bristles were not examined and interpreted in the context of the observed drag and lift reduction. A dynamically scaled robotic model mimicking clap and fling was used to comparatively test bristled wing models with varying inter-bristle spacing at Re on the order of 1-10. Leaky inter-bristle flow in the direction opposite to wing motion was observed in all bristled wing models during clap and fling, resulting in drag reduction. Vorticity at the leading and trailing edges decreased with increasing inter-bristle spacing, resulting in greater loss of lift. Shear layers formed around the bristles reduced the effective gap through which fluid leakage occurred, minimizing the loss of lift in bristled wings.