Meeting Abstract
Tiny insects with body lengths under 1 mm, such as thrips and fairyflies, use bristled wings for flapping flight at Reynolds number (Re) on the order of 10. Thrips have also been observed to use wing-wing interaction via the clap and fling mechanism. We examine how varying the gap or spacing between a pair of bristles (G) relative to bristle diameter (D) impacts the forces and flow structures generated during wing-wing interaction. The bristle gap to diameter (G/D) ratios in a number of thrips species were quantified from published data. Physical models of bristled wing pairs with G/D in the range of 5-17 and a geometrically equivalent solid wing pair were developed for this study. These physical models were tested using a dynamically scaled robot that was programmed to execute clap and fling kinematics. Non-dimensional lift and drag coefficients were estimated from strain gauge measurements of time-varying forces. Phase-locked particle image velocimetry (PIV) measurements were used to examine flow through the bristles. Chordwise PIV measurements were used to visualize leading and trailing edge vortices formed over the wings during flapping. The results show that both lift and drag forces reduce with increase in G/D. However, spanwise flow around the bristles reduce the drag force by a larger proportion relative to the reduction in lift force, thus increasing the lift to drag ratio.
