Strong vortex gusts are a primary cause of flight-vehicle control destabilisation. To investigate the underlying mechanism, direct numerical simulation and impulse theory are employed to systematically analyze the unsteady flow characteristics and aerodynamic performance of a vortex dipole impinging on a NACA0012 airfoil at zero angle of attack. The study finds that the centerline height of the vortex dipole is the core parameter determining the airfoil force and moment characteristics: the drag reaches its maximum when it is level with the leading edge; the lift, moment, and thrust peak when it is slightly above the leading edge; as the height increases further, the vortex-body interaction decays, and the aerodynamic disturbances approach zero. The physical mechanisms differ significantly across heights. In level case, the vortex dipole splits, and the induced secondary vortices combine with it to form a new dipole. This new structure interacts with the airfoil again through self-induced motion, generating oscillatory drag. In slightly high case, the negative-signed primary vortex interacts directly with the airfoil, causing its deformation, weakening, and trajectory deviation. This process leads the thrust to change from a peak to a trough, while the lift and moment undergo an asymmetric evolution from small negative values to large positive values. In high-spacing case, the motion path of dipole is almost unaffected by the presence of the airfoil. Analysis based on impulse theory further reveals the intrinsic relationship between aerodynamic forces and vortex motion: during collision, the change in the primary vortex impulse dominates the force generation; in non-collision cases, the primary vortex impulse remains nearly constant, and the rate of change of impulse from the induced secondary vortices determines the airfoil forces. Quasi-3D simulations with spanwise periodic boundary conditions reveal that an over-limit spanwise computational domain triggers strong 3D flow effects, causing remarkable attenuation of peak aerodynamic force and moment coefficients.

The assessment of aerodynamic performance is crucial for designing Flapping-Wing Micro Air Vehicles (FWMAVs), yet limited research has addressed the prediction and analysis of flexible wing aerodynamics during the preliminary design phase. This study proposes an efficient prediction method for the aerodynamic characteristics of flexible flapping wings. A conical surface model is introduced to mimic wing deformation, and the unsteady panel method is employed to predict aerodynamic characteristics. The wing deformation characteristics, the influence of membrane tightness on aerodynamics and the control moments as well as additional moments resulting from coupled control based on the two-winged FWMAV configuration have been investigated. Results indicate that the current prediction method effectively captures the deformation and aerodynamic characteristics of flexible flapping wing. A relatively slack membrane enhances aerodynamic efficiency when the lift is satisfactory. The roll, pitch, and yaw moments correlate linearly with the root vein deflection angle in baseline case, while excessive membrane tension reduces or reverses control effectiveness. The additional roll moment resulting from coupled pitch and yaw controls is significantly greater than the other two additional moments. The findings provide valuable insights for the aerodynamic and control design of flexible flapping wings.

Hover-capable flapping-wing micro air vehicles (FWMAVs), inspired by insects or hummingbirds, exhibit remarkable flight characteristics such as hovering capability, high aerodynamic efficiency at low Reynolds numbers, and strong stealthiness, offering diverse potential applications in disaster rescue, emergency response, and environmental monitoring. However, the aerodynamic forces and efficiency of their flapping wings still lag considerably behind those of their biological counterparts, adversely affecting the endurance and payload capacity of FWMAVs and significantly limiting their practical applications. This paper provides a comprehensive overview of hover-capable FWMAVs, with a focus on current research progress, theoretical and experimental methods for aerodynamic analysis, the high-lift mechanisms of insects and their applications in FWMAVs, as well as aerodynamic design methods and performance evaluation of flapping wings. The review highlights key design parameters for achieving high lift, high aerodynamic efficiency, and low noise, and elucidates the impact of these parameters on the performance of FWMAVs. Finally, future trends in aerodynamic design for hover-capable FWMAVs are discussed, offering valuable guidance for future research in this field.