Three-dimensional numerical simulations of a four-wing flapping micro aerial vehicle (FMAV) with actual experimentally captured wing membrane kinematics have been performed using an immersed boundary method Navier-Stokes finite volume solver. To successfully simulate the clap and fling motion involving the wing intersection, the numerical solver has been specifically modified to use a newly improved interpolation template searching algorithm to prevent divergence. Reasonable agreement was found between the numerical and experimental results, with the first and second force peaks from the experimental results well captured by the simulations, which was not possible in the past. Moreover, a "V-shaped linked" vortex was observed, which was similar to the vortical structures found in other experiments and simulations. A wing drag analysis showed that the drag magnitude of the clap and fling configuration was about 2.5 times that of the single-wing configuration. Visualizations of the flowfields through pressure contours and vortical isosurfaces led to a better understanding of the underlying flapping-wing aerodynamics. The ability to accurately simulate the FMAV with flexible wings opened up many opportunities for further FMAV design-related problems.@en

A robust and efficient dynamic grid strategy based on an overset grid coupled with mesh deformation technique is proposed for simulating unsteady flow of flapping wings undergoing large geometrical displacement. The dynamic grid method was implemented using a hierarchical unstructured overset grid locally coupled with a fast radial basis function (RBF)-based mapping approach. The hierarchically organized overset grid allows transferring the grid resolution for multiple blocks and overlapping/embedding the meshes. The RBF-based mapping approach is particularly highlighted in this paper in view of its considerable computational efficiency compared with conventional RBF evaluation. The performance of the proposed dynamic mesh strategy is demonstrated by three typical unsteady cases, including a rotating rectangular block in a fixed domain, a relative movement between self-propelled fishes and the X-wing type flapping-wing micro air vehicle DelFly, which displays the clap-and-fling wing-interaction phenomenon on both sides of the fuselage. Results show that the proposed method can be applied to the simulation of flapping wings with satisfactory efficiency and robustness.@en

A numerical study was carried out to investigate the effect of chordwise flexion on the propulsive performance of a two-dimensional flexible flapping wing. The wing undergoes a prescribed sinusoidal heaving motion with a local deflection. A deformable overset grid dynamic mesh method was employed to implement the motion of the grid instantaneously. The effect of flexural pattern, flexural amplitude and flapping frequency in terms of Strouhal number are evaluated. Unsteady flow around the wing is computed using an in-house developed Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver. The results show that the different flexural patterns will create different flow fields, and thus the thrust generation will be significantly varied. The thrust and propulsive efficiency do not increase monotonically with the flexure amplitude while a peak value is revealed. It is found that the wake vortices after the flapping motion assembly behave as a reverse von-Karman vortex street, which can principally create thrust. The thrust is found to increase with increasing Strouhal number. Propulsive efficiency is beneficial from the chordwise flexibility and peaks within the range of 0.2