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

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 degrees, was selected, because of its similar to 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. (C) 2021 Elsevier Masson SAS. All rights reserved.