Abstract: Insects including dragonfly with powerful maneuvering performance are accounted as the best experts in aviation. However, ornithopters inspired by insects have much poorer maneuverability than insects. To find out the maneuvering aerodynamics of insects, a numerical study of the 3D aerodynamic forces and moments of a dragonfly in asymmetric flapping is carried out using the Finite Volume Method (FVM). The total aerodynamics of the dragonfly, aerodynamics of each wing, pressure distributions and vorticity are analyzed at different flapping amplitude. The results indicate that maneuvering flight to one side can be achieved by increasing the flapping amplitude of the two wings on the other side. Compared with the hindwing, the flapping amplitude has greater effect on the lift, thrust, roll and yaw moments of the forewing, and smaller effect on the lateral force. The instantaneous drag, lateral force, yaw and pitch moments are influenced by the flapping amplitude during the whole flapping cycle, and the flapping amplitude affects the instantaneous lift and roll moment obviously in down-stroke. The flapping amplitude changes the leading edge vortex, trailing vortex and the pressure difference between the upper and lower surfaces. In down-stroke, there is a slant angle between the wings and the symmetric plane of the dragonfly to lead to greater lateral force, and in up-stroke, the wings are almost vertical to the symmetric plane, which means the generation of smaller lateral force. These results can offer some guidance for attitude control and aerodynamic design of ornithopters.

Key words: dragonfly, asymmetric flapping, aerodynamic characteristics, lateral force, flapping amplitude, 3D aerodynamic moment