Aerodynamics of tiny wings show how small insects fly by wing acceleration

Unlike the smooth wings of an eagle, some small insects have bristled wings less than half a millimeter long. Instead of flapping, these wings move with a rowing motion to allow flight, creating the drag forces needed to allow these insects, which include fairyflies, thrips and tiny wasps, to move vertically.

While bristled wings have been previously studied, researchers still do not understand how they produce large aerodynamic forces by rapid wing acceleration. Wu et al. investigated these forces with numerical simulations and simple model wings.

“Studying the aerodynamic characteristics of bristled wings in fast acceleration motion is of great significance for understanding the flight mechanism of the smallest insects,” said co-author Mao Sun. “The results might also be used in designing millimeter-scale microair vehicles in the future.”

With numerical simulations, the researchers examined the flow structures around each bristle in a modeled wing as well as the interference of flows between bristles. They found a bristled wing produced very large and unsteady drag, like what happens with a flat-plane wing. However, unlike a flat wing, the mechanism of force production for bristled wings was a strong viscous effect of the flows creeping around the bristles.

“The bristled wing has the advantages of light weight and could generate aerodynamic forces similar to that of the membrane wing, which potentially inspires the design and manufacture of millimeter-scale aircrafts in the future,” Sun said.

The researchers plan to investigate the flow interactions between two bristled wings. Due to the small space between the wings of tiny insects, the effects between wings could be influential on drag forces.

Source: “Unsteady aerodynamics of a model bristled wing in rapid acceleration motion,” by Yu Kai Wu, Yan Peng Liu, and Mao Sun, Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0067169 .