Effects of wing kinematics, corrugation, and clap-and-fling on aerodynamic efficiency of a hovering insect-inspired flapping-wing micro air vehicle

Abstract

A flapping-wing micro air vehicle (FW-MAV) operating with aerodynamically optimal wing configuration and kinematics may save energy and thus prolong flight time. In this work, we use a computational-fluid-dynamic method to investigate the effects of wing kinematics, corrugation structures, and clap-and-fling on the aerodynamic efficiency of our hovering two-winged FW-MAV (KUBeetle). From the measured reference wing kinematics, we generated several different wing kinematics, considering the effect of spanwise twist and chordwise camber that produce high lift-to-drag ratio (L/D). Among the investigated cases, the modified wing kinematics version 3, which includes both camber and twist with an average angle of attack of about 37°, was selected, because of its ∼24% improvement of L/D, while maintaining similar lift to the measured reference wing kinematics. The results also showed that the camber plays a role in the improvement of both lift and L/D, which improvements are approximately (16.7 and 10.6)%, respectively. We then used wing kinematics version 3 to investigate the effects of various leading-edge corrugation structures. Based on the results of lift and L/D, we proposed a wing with distributed wing corrugations along the wingspan, which slightly augments the L/D by 2%. In addition, to see how the clap-and-fling behavior contributes to the aerodynamic efficiency, its effects on lift and drag generation were examined. We found that the clap-and-fling enhanced lift by 5%, but increased drag by 9%, resulting in a 4% reduction of the L/D for both the measured and the modified wing kinematics. Thus, the lift-augmented clap-and-fling is inefficient for FW-MAVs. Finally, the study confirmed that the wing with distributed wing corrugations using wing kinematics version 3 without clap-and-fling presented at the stroke reversals is preferable for the high aerodynamic efficiency of the KUBeetle robot, with 31% improvement in L/D.