Experimental and numerical study of dragonfly ( Anax parthenope julius ) in climbing flight: Aerodynamic mechanisms for stable ascent

Dragonflies' exceptional climb capability plays a crucial role in essential survival behaviors such as predation and evasion. However, the climb performance in aerial vehicles remains relatively weak, posing challenges in achieving efficient and stable vertical ascent. To investigate the body motion patterns and wing flapping strategies during climbing flight, this study first conducts biological observations to obtain basic biological characteristics and key climbing parameters. Based on the observational data, numerical simulations are performed to explore aerodynamic performance during ascent. The flow field structures are analyzed through flow visualization. The results show that the dragonfly's climbing process can be divided into four stages, with the average flapping frequency being 28.0 Hz and the total duration being approximately 0.82 s. The ascent is predominantly vertical, with slight backward flight and turning near the end. The angle of attack is essential for regulating flight posture and speed. Meanwhile, by adjusting the flapping plane tilt angle, deviation angle, and amplitude, the dragonfly maintains high lift and stable climbing through the synergistic effects of typical vortex structures such as leading-edge vortices. During the rapid-ascent phase, a significant pressure difference occurs on the wing surfaces along with delayed stall, and rotational circulation is also formed, both of which are key mechanisms for enhanced aerodynamic force generation. Furthermore, the dragonfly dynamically balances lift and flight maneuverability by modulating the phase difference between the forewings and hindwings, with their interaction resulting in a maximum aerodynamic force increase of 25.1%, highlighting the sophisticated aerodynamic strategies during climbing flight.