Numerical investigation of the effects of wing bristles and wing flexibility on the forward flapping aerodynamics of the smallest flying insects

We used computational fluid dynamics to investigate the effects of bristles and wing flexibility on the forward flapping aerodynamics of the smallest flying insects. The immersed boundary method was used to solve the fully coupled fluid-structure interaction problem of a pair of flexible wings immersed in a three-dimensional viscous fluid. To determine the effects of bristles, three wings were considered that ranged from least to most bristled. The results suggest that at Re relevant to small insect flight, rigid-bristled wings generate nearly as much average vertical force and thrust as rigid-solid wings while providing the benefit of lower wing mass. To investigate the effects of wing flexibility, four flexible-solid wings with spanwise flexibility were considered and a new parameter called deflection angle was defined to characterize their flexibility. Based on the results, it appears that at Re pertinent to tiny insect flight, adding a high degree of spanwise flexibility to rigid-solid wings deteriorates their average vertical force and thrust to a large extent. For moderately spanwise-flexible wings, the results suggest that they generate nearly as much average vertical force as their rigid counterparts while providing the benefit of increased average thrust.