Water-treading motion for three-dimensional flapping wings in Hover

Flapping-wing micro air vehicles are not confined to undergoing the normal-hovering motion implemented by flying insects. In this study, the water-treading motion, which originates from aquatic propulsion, is studied in terms of its feasibility as an alternative wing motion for micro air vehicles. Experimental measurements and numerical simulations have been conductedon a rigid three-dimensional flapping wing undergoing normal-hovering and water-treading motions, with the aim of identifying which motion profile is superior from a purely aerodynamic point of view. Results from the present parametric study show that the water-treading motion offers two main advantages over normal-hovering motion. Firstly, the leading-edge vortex generated by the water-treading motion tends to be more stable, resulting in higher-lift generation. Secondly, whereas normal-hovering motion enters a high-angle-of-attack high-drag configuration during stroke reversal, the water-treading motion avoids this unfavorable configuration. As a result, the water-treading motion offers superior aerodynamic performance in terms of lift generation and efficiency. Hence, it may be an attractive alternative for efficient micro-air-vehicle design.