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The dynamic deformation data were further used to calculate the inertial forces by regarding the wing as a system of particles to take into account the wing flexibility. The dynamic deformation data were subsequently interpolated and embedded into the CFD solver to account for the aeroelastic effects. To obtain the real deformation pattern of the flapping wing, the digital image correlation technology was used to measure the dynamic deformation of the wing. The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment. In some cases they remain isolated but orbit other vortical structures, while in other cases they pair with other vortical structures, and finally when the reduced frequency and asymmetry values are high enough the vortex array shows interaction between cycles. The number of secondary vortices and the downstream evolution of the vortices depends on the symmetry value. Multiple vortices are formed during the “slow” portion of the pitching motion. The asymmetric cases show that a single vortex is formed during the “fast” portion of the pitching motion. The data show that for the 50/50 (symmetric) motions two alternating sign vortices, with equivalent strength, are formed as expected. Pitching symmetries of 50/50, 40/60 and 30/70 are studied, where the symmetry is defined by the fraction of the cycle spent in the pitch down versus pitch up motion. The airfoil is pitched about the quarter chord point with an amplitude of ±4° at reduced frequencies of k = 2.6–5.8 at a Rec = 12000. Particle Image Velocimetry (PIV) is used to quantify the flow field around a NACA0012 airfoil undergoing small amplitude, high frequency asymmetric pitching. This work focuses on the wake patterns developed due to asymmetric pitching. Studies investigating the effects of asymmetric motion are more limited. Past work has centered on the flow fields generated by symmetric pitching of the airfoil. The flow around, and in the wake of, pitching airfoils has received renewed interest due to its potential for thrust production at low Reynolds numbers. The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance. The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon. The defined motion has similar lift performance with the bio-inspired kinematics, while it consumes more energy and generates less thrust. The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke, while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke. Meanwhile, the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion. The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle. It is found that the cambered owl-like airfoil can enhance lift during the downstroke. The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil. A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison. The bio-inspired kinematics consist of plunging and pitching movement.

The overset mesh technique is used to deal with the large range movements of flapping airfoils. In this paper, the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated. However, the aerodynamic mechanism of birds' flapping wing kinematics still lacks in-depth understanding. Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention.