Numerical simulation on aerodynamic performance of bird-like flapping wing with slotted-tip

Birds are highly capable and maneuverable fliers, and some of their unique traits are still not currently shared with current small unmanned aerial vehicles. One feature of bird wings, wingtip slots, where the outer primary feathers of birds split and spread vertically, are considered a product of improving the aerodynamic performance during the evolution of birds. It is essential to draw the optimal layout of the wingtip by studying the effects of its parameters on aerodynamic characteristics of the wing and apply it to flapping-wing MAV's design process. In this paper, the Reynolds-Averaged Navier-Stokes method (RANS) is utilized to investigate the mechanism of the effects of biomimetic slotted wingtips with different geometrical parameters (number of slots) and spatial distribution parameters (dihedral) on tip vortex structure and aerodynamic performance. After grid independence verification is accomplished, parametric geometric models of the biomimetic slotted wing are established and computation meshes are calculated. Based on models established in this paper, the results show that wingtip slots can retard the chordwise pressure gradient of the wing and mitigate wing stall, thus reduce the complexity of flight control and sensitivity to flight control errors. Adding dihedral to slotted wing gets better stall mitigation, while obtains lift increase and drag reduction in the pre-stall region, thus increases the lift-to-drag ratio, which is helpful to improve gliding capabilities under the limitation of wing span. The slotted wing tip with 45°dihedral can increase lift by 2.2%, reduce drag by 7.7%, and increase the lift-to-drag ratio by 10.3%. Meanwhile, maximum achievable lift and longitudinal stability of non-planar slotted wing obtain considerable improvement.