Study on aerodynamic performance of a bio-inspired flapping wing under the effect of anti-reversal duration

This paper proposes a corrected trapezoid model for pitching (featuring flapping at the stroke ends and motionlessness during intervals) and an anti-trapezoidal model for translation (featuring motionlessness at the stroke ends and motion during intervals), collectively abbreviated as 'T'. The aerodynamic characteristics of a bio-inspired flapping wing are investigated using computational fluid dynamics, with a traditional NACA0012 airfoil employed as a reference model. Numerical simulations are conducted to examine the influence of anti-trapezoidal duration (i.e., the total stationary time in a stroke), flapping modes (i.e., combinations of motion functions across multiple degrees of freedom), and sweeping amplitude on aerodynamic performance. The results indicate that the anti-trapezoidal model significantly affects aerodynamic behavior, with the 'T-T-H' mode (where 'H' denotes the harmonic model) yielding the optimal performance among all cases. In contrast, the duration exerts only a minor influence. Regarding the asymmetrical ratio, an increase in this coefficient is found to enhance aerodynamic propulsion, suggesting that the symmetrical durations of upstroke and downstroke are beneficial for flight. This improvement is attributed to the delayed stall of the leading-edge vortex and the shedding of the trailing-edge vortex. Across all cases involving the anti-trapezoidal sweeping model, the incorporation of anti-trapezoidal motion in both plunge and pitching improves average lift and propulsion, indicating that the 'T-T-T' mode is preferable for flapping flight. Moreover, increasing the sweeping amplitude enhances aerodynamic performance, as supported by pressure and vorticity contours. These findings provide a comprehensive understanding of the variations in aerodynamic characteristics of bio-inspired flapping wings, offering valuable insights for the design and development of flapping-wing drones.