A mechanical investigation of flapping-wing flight through reduced-order modeling

Abstract

Micro air vehicles are a class of unmanned aerial vehicle far smaller than conventional vehicles. Due to their maneuverability and small form-factor, these craft show great promise in a myriad of applications, ranging from artificial pollination to mapping cave systems to search-and-rescue. When established platforms like multirotors are reduced down to these sizes, aerodynamic scaling effects has a deleterious impact on vehicle performance. To overcome this, we turn to insect flight for inspiration. Flying insects utilize flapping wings to achieve flight, and do so efficiently. Capable of migrating huge distances and performing advanced aerobatics, insects have many adaptations that help them fly. Highly- flexible wings yield aerodynamic and energetic benefits while reducing the reducing the weight the insect needs to carry. Potential energy storage in the thorax enables them to recoup effort spent driving their wings, and fly farther. Despite the benefits afforded by flapping wings, they are still not fully understood. Study of flapping-wing flight is challenging owing to the high-speed, large-amplitude wing motion and aeroelastic deformation of the wings, making measurement of aerodynamic forces difficult. Computational methods allow us to overcome these obstacles. High-fidelity modeling enables accurate prediction of the airflow and pressures acting on the wing, and of the fluid-structure interaction present, however the large computational cost makes them unsuited for parametric studies. In this work, a reduced-order model is developed to study the fluid-structure interaction in flexible flapping wing systems. Bulk aerodynamic forces are accurately predicted with short solutions times, enabling parametric studies to be conducted. The effect of variable rigidity is investigated in 2D and 3D wings, and results compared to high-fidelity methods. Thorax dynamics are added in order to study elastic energy recycling. We find that moderate levels of wing flexibility improve the performance of flapping wings by lowering the energetic requirements, and that optimized system parameters can reduce power consumption through elastic energy recycling and resonance excitation.