Aerodynamic characteristics of tandem self-propelled flapping wings with asymmetric pitching motion

Birds and insects often fly in flocks, and understanding the interaction mechanisms between their wings is key to studying the complex flow dynamics in flocking flight. This study numerically investigates the aerodynamic characteristics of tandem, self-propelled flapping wings using the lattice-Boltzmann method. We explored the effects of varying the angle of attack and pitching motion amplitude on the aerodynamic performance, focusing on the lift and propulsion efficiency. Our findings show that smaller angles of attack (0 degrees, 5 degrees, and 10 degrees) enable stable flight, whereas larger angles (15 degrees and 20 degrees) fail to do so in most cases. Among the stable configurations, a 5 degrees angle of attack provided the best aerodynamic performance. Additionally, when the angle of attack was fixed, increasing the pitch amplitude had a minimal effect on the fore wing's aerodynamics. However, the hind wing's lift coefficient increases relative to a single wing, improving the lift and lift efficiencies while decreasing the propulsion efficiency, although it remains higher than that of a single wing. The power consumption also increased but remained lower than that of the single-wing case. At maximum pitch amplitude, the system's lift approaches that of a single wing, but with higher lift and propulsion efficiency and lower power consumption. These results suggest that larger pitching amplitudes enhance the aerodynamic performance and energy efficiency, providing insights into the lift and thrust generation principles in flock flight. This study can guide the design of bionic micro-air vehicles (MAVs).