Experimental investigation on tip-vortex flow characteristics of novel bionic multi-tip winglet configurations

Five bionic multi-tip winglet configurations, inspired by basic feather shapes and wingtip postures of birds, were designed to suppress the tip-vortex structures around their wingtips. Each of the bionic multi-tip winglet configurations consists of multiple novel feather-shaped winglets and looks like a dihedral (or non-planar) wingtip shape. The influence of the distribution density and chord-directional gap for the feather-shaped winglets on the tip-vortex flow characteristics was investigated experimentally at Re = 83 166. The results reveal that the vorticity levels of the tip-vortex structures in the near-wake region can achieve effective suppression by improving the feather-shaped winglets’ distribution density at the wingtip of the bionic wing configuration. The maximum proportions of the induced drag relative to the total drag for the bionic wing configurations I, II, and III are 25.54%, 21.05%, and 19.47%, respectively. The variation of the feather-shaped winglets’ distribution density significantly affects the lift–drag efficiency of the bionic wing configuration. However, the increase in the feather-shaped winglets’ mounting gap weakens the tip-vortex suppression effect for the bionic wing configuration (equipped with the three feather-shaped winglets) to some degree. The maximum proportions of the induced drag relative to the total drag for the bionic wing configurations IV and V are 27.28% and 28.32%, respectively. Compared with the bionic wing configuration I, the slightly worse aerodynamic performance for the bionic wing configurations IV or V (with the larger feather-shaped winglets’ mounting gap) is closely related to its weaker tip-vortex suppression ability.