Effect of Coupled Wing Motion on the Aerodynamic Performance during Different Flight Stages of Pigeon

Birds achieve remarkable flight performance by flexibly morphing their wings during different flight stages. However, due to the lack of experimental data on the free morphing of wings and the complexity of coupled motion in aerodynamics studies, the intricate kinematic changes and aerodynamic mechanisms of wings during various flight stages still need to be explored. To address this issue, we collected comprehensive data on free-flight pigeons (Columba livia). We categorized the wing kinematic parameters during the takeoff, leveling flight, and landing stages into 5 kinematics parameters: flap, twist, sweep, fold, and bend. Based on this, we established a 3-dimensional pigeon wing model, defined its coupled motion using rotation matrices, and then used the computational fluid dynamics method to simulate the coupled motion in the 3 flight stages. We analyzed and compared the kinematic parameter changes, aerodynamic forces, and flow structures. It is found that, within a wingbeat cycle, pigeons during the takeoff stage cause the leading-edge vortex to attach earlier, enhancing instantaneous lift to overcome gravity and achieve ascending. During the leveling flight stage, the pigeon's average lift becomes stable, ensuring a steady flight posture. In the landing stage, the pigeon increases the wing area facing the airflow to maintain a stable landing posture, achieving a more minor, consistent average lift while increasing drag. This study enhances our understanding of birds' flight mechanisms and provides theoretical guidance for developing efficient bio-inspired flapping-wing aerial vehicles.