Tip-vortex flow characteristics investigation of a novel bird-like morphing discrete wing structure

Abstract

A bird-like morphing discrete wing, inspired by primary feathers of birds’ wings, was designed to control the wing-tip vortex strength. The influence of both the morphing process and discrete (non-continuous) surface feature for the bird-like wing structure on the tip-vortex flow characteristics was investigated in detail at Re = 87 000. The results reveal that the morphing process of the bird-like discrete wing structure can achieve the effective control of the core vortex strength by changing the flow structures around the tip-vortex core center(s). The induced drag yielded by the bird-like morphing wing structure is tightly related to its vorticity distribution in the near-wake region. Moreover, compared with the fully extended fixed-wing model with a continuous surface structure, the bird-like discrete wing model with the fully extended morphing state can suppress the core vortex strength by destroying the tip-vortex merging process. Meanwhile, the core vortex strength of the fully extended discrete wing model decays more sharply with the increase in x/c. The maximum proportions of the induced drag relative to the total drag for both the discrete and continuous wing models with the fully extended shape are 14.33% and 19.97%, respectively. However, the fully folding process of the bird-like wing structure significantly weakens the induced-drag reduction effect of the discrete surface structure. The maximum proportions of the induced drag relative to the total drag for both the discrete and continuous wing models with the fully folded shape are 17.59% and 18.41%, respectively.