Aerodynamic performance and vortex mechanisms of a bird-like airfoil with coupled pitching, plunging, and sweeping motions

Bird wings exhibit sophisticated coupling of plunging, sweeping, and pitching motions to achieve high aerodynamic performance. To reveal the underlying aerodynamic and vortex-dynamic mechanisms, this study numerically investigates the effects of pitching amplitude αm on the lift, thrust, power consumption, and efficiency of a bird-inspired airfoil under various plunging–sweeping trajectories. The trajectory is defined by the phase difference φ1 and amplitude ratio Xm/Ym between plunging and sweeping motions. A validated unsteady Reynolds averaged Navier–Stokes solver is employed to analyze aerodynamic performance and vortex evolution. Results show that pitching motion exerts a trajectory-dependent regulatory effect on both lift and thrust. At low φ1 (high-lift mode), pitching suppresses dynamic stall and reduces lift but converts drag into thrust; at high φ1 (cruise mode), pitching compensates angle-of-attack deficiency, stabilizes leading-edge vortex (LEV) evolution and enhances lift at medium-to-low Xm/Ym. The balanced preferred pitching amplitude of 32° within the investigated parameter range is identified. Moderate pitching (28°–36°) maintains the effective angle of attack αeff in the optimal 35°–45° range, enabling stable LEV attachment, suppressed secondary vortices and delayed trailing-edge vortex formation. Quantitatively, optimal pitching prolongs LEV attachment by 33%, reduces secondary vortices contribution to below 15%, and improves propulsive efficiency by over 40%. These findings clarify the coupling relationships among pitching amplitude, trajectory kinematics, aerodynamic performance and vortex dynamics, providing theoretical support for bio-inspired flapping-wing vehicle design.