Clap-and-Fling Mechanism in Non-Zero Inflow of a Tailless Two-Winged Flapping-Wing Micro Air Vehicle

The aerodynamic performance of clap-and-fling mechanism in a KU-Beetle—a tailless two-winged flapping-wing micro air vehicle—was investigated for various horizontal free-stream inflows. Three inflow speeds of 0 (hovering), 2.52 m/s and 5.04 m/s corresponding to advance ratios of 0, 0.5 and 1 were considered. The forces and moments for two wing distances of 16 mm (in which the clap-and-fling effect was strong) and 40 mm (in which the clap-and-fling effect was diminished) were computed using commercial software of ANSYS-Fluent 16.2. When the advance ratio increased from 0 to 0.5 and 1, the lift enhancement due to clap in the down-stroke reversal increased from 1.1% to 1.7% and 1.9%, while that in the up-stroke reversal decreased from 2.1% to −0.5% and 1.1%. Thus, in terms of lift enhancement due to clap, the free-stream inflow was more favorable in the down stroke than the up stroke. For all investigated inflow speeds, the clap-and-fling effect augmented the lift and power consumption but reduced the lift-to-power ratio. The total contributions of the fling phases to the enhancements in lift, torque, and power consumption were more than twice those of the clap phases. For the advance ratio from 0 to 0.5 and 1, the enhancement in average lift slightly decreased from 9.9% to 9.4% and 9.1%, respectively, and the augmentation in average power consumption decreased from 12.3% to 10.5% and 9.7%. Meanwhile, the reduction in the average lift-to-power ratio decreased from 2.1% to 1.1% and 0.6%, implying that in terms of aerodynamic efficiency, the free-stream inflow benefits the clap-and-fling effect in the KU-Beetle.