Computational study on the hovering mechanisms of a chordwise flexible wing

The flexion effect of a flexible wing during the hovering flight is systematically studied by using computer simulations when Reynolds number is kept at 140. The aerodynamic forces and flow vortex are investigated by solving the two-dimensional time-dependent incompressible Navier-Stokes equations using the finite volume method. The wing is modelled as a thin plate which has a rigid leading portion and a flexible aft part. The simulations are performed for a variation of the location of rotational centre and the amplitude of the flexion, and the corresponding changes of the aerodynamic forces and vortex shedding mechanism in the wake structure are investigated. Form the quantitative comparisons, the present simulations reveal that a moderate flexion during the hovering fly can provide a better performance for a flapping wing, while an excessive flexion will lead the aerodynamic performance become worse. Though the flexion does not change the force trace of the hovering wing, the magnitude of the instantaneous peak forces and mean periodic forces are definitely changed by the chordwise deformation. Compared with a rigid hovering wing, the dynamic flexion during hovering alters the intensity of the leading edge vorticity and the transfer direction of the wake. Here, the present results indicate that the aerodynamic forces can be altered by adding some deformation characteristics to the trailing edge of the wing. Furthermore, the appropriate flexion can be used to alter the aerodynamic performance of a wing and will be helpful for design and control of the flexible microflying vehicles.