Unsteady fluid–structure interaction mechanisms in a flapping plate under flexible deformation

An isotropic dragonfly-inspired flat-plate model with prescribed kinematics is established. Based on fluid–structure interaction simulations, the unsteady aerodynamic mechanism of the flexible flat plate in flapping flight is investigated. Compared with a rigid flat plate, flexible deformation increases the cycle-averaged lift by 83.9%. The effects of flexible deformation on aerodynamic forces are further analyzed from both temporal and spatial perspectives. To explore the influence of the degree of flexibility, numerical simulations are performed for flexible plates with different stiffness. The results show that when the natural frequency of the plate approaches the flapping frequency or its harmonics, resonance occurs, leading to amplified flexible deformation and significantly affecting the aerodynamic forces. During the downstroke, the lift peak is jointly regulated by the prescribed kinematics and the release of strain energy. When the natural frequency lies between the first and second harmonics of the flapping frequency, additional lift can be generated during the upstroke through localized downstroke motion.