Optimization of Flexible Flapping Wings for Thrust and Efficiency

View Video Presentation: https://doi.org/10.2514/6.2021-2570.vid For a flexible wing in flapping motion, different types of deformation, such as bending and twisting, may contribute differently to its thrust power and efficiency. The study of the impact from the deformation gets more challenging when many other control parameters in the original flapping motion (of the rigid wing) are involved. With the time-varying feature of all these control parameters, it is impractical and unnecessary to have a complete parametric study for the optimization of flexible flapping wings for either thrust power or efficiency. An adjoint-based approach, with the implementation of non-cylindrical calculus for moving boundary problems, has been developed in our earlier study for the optimization of rigid-wing flapping. A similar approach is taken here to study the impact of flexibility on the aerodynamic performance of flapping wings. The optimization in spanwise bending on top of a flapping wing in the motion optimized for a rigid wing shows that the bending may double the thrust power at the price of a small reduction of efficiency. On the other hand, the optimization of twisting can help the flexible wings maintain a large thrust with a much lower total energy consumption. The analysis of pressure distribution and physical modeling reveal more details on the mechanism of how bending and twisting play their different roles in this scenario.