Aerodynamic interaction of bristled wing pairs in fling

Tiny flying insects of body lengths under 2mm use the clap-and-fling mechanism with bristled wings for lift augmentation and drag reduction at a chord-based Reynolds number (Re) on O ( 10 ). We examine the wing-wing interaction of bristled wings in fling at Re = 10 as a function of initial inter-wing spacing (delta) and degree of overlap between rotation and linear translation. A dynamically scaled robotic platform was used to drive physical models of bristled wing pairs with the following kinematics (all angles relative to vertical): (1) rotation about the trailing edge to angle theta (r), (2) linear translation at a fixed angle (theta (t)), and (3) combined rotation and linear translation. The results show that (1) the cycle-averaged drag coefficient decreased with increasing theta (r) and theta (t) and (2) decreasing delta increased the lift coefficient owing to increased asymmetry in the circulation of leading and trailing edge vortices. A new dimensionless index, reverse flow capacity (RFC), was used to quantify the maximum possible ability of a bristled wing to leak the fluid through the bristles. The drag coefficients were larger for smaller delta and theta (r) despite larger RFC, likely due to the blockage of inter-bristle flow by shear layers around the bristles. Smaller delta during early rotation resulted in the formation of strong positive pressure distribution between the wings, resulting in an increased drag force. The positive pressure region weakened with increasing theta (r), which in turn reduced the drag force. Tiny insects have been previously reported to use large rotational angles in fling, and our findings suggest that a plausible reason is to reduce drag forces.

Automated summary

By studying the interaction between bristled wings of tiny flying insects, researchers have found that adjusting the rotational and linear translation angles can reduce drag and increase lift during flapping. Results show that smaller initial spacing between wings leads to higher drag coefficients, while increasing the rotational angle can reduce drag. This study suggests that tiny insects use large rotational angles during flapping to reduce drag forces.