Sweep-angle-regulated aerodynamic interference mechanisms in dragonfly tandem wings

Dragonflies achieve remarkable flight performance through their unique tandem-wing configuration; however, the aerodynamic interference mechanisms regulated by wing morphological parameters remain insufficiently understood. In this study, numerical simulations based on prescribed flapping kinematics were conducted to investigate the effects of sweep angle on the aerodynamic interactions between the forewing and hindwing of dragonfly-inspired tandem wings. Variations in aerodynamic forces, vortex structures, and aerodynamic efficiency were analyzed. The results indicate that the sweep angle is a key parameter governing the coupling between the forewing wake and the hindwing leading-edge vortex (LEV). When the sweep angle remains small (δ ≤ 10°), strong aerodynamic interactions exist between the two wings. As the sweep angle increases, the relative spatial relationship between the hindwing and the forewing wake changes, thereby weakening the inter-wing interaction. More importantly, the dominant interference mechanism exhibits a pronounced dependence on the forewing–hindwing phase difference. Under in-phase flapping, the forewing trailing-edge vortex and the hindwing LEV form an inter-wing dipole vortex structure that suppresses the development of the hindwing LEV. For 45° ≤ ψ ≤ 135°, the aerodynamic response of the hindwing is governed by the pronounced strip-shaped disturbance region generated as the forewing root vortex sweeps across the hindwing surface. When the phase difference increases to 180°, the dominant interference shifts to the wrapping interaction of the forewing tip vortex with the hindwing, which modifies the vortex structures and pressure distribution. Overall, sweep angle regulates tandem-wing aerodynamic performance by controlling the phase-dependent interaction pathways between distinct forewing wake structures and the hindwing.