The effect of bionic 3D printed structure morphology on skin friction

Dragonfly has remarkable flight efficiency, with unique wing structural properties such as the surface topological vein structures, corrugation, etc. The object of this paper is to identify how the polygonal patterns of the samples with bionic wing veins affected the skin friction. Four kinds of polygonal three-dimensional (3D) patterns were designed and fabricated by additive manufacturing technology, and the skin friction coefficients (C-f) of various models were measured by the wind channel experiments. The quantitative effects of models on C-f with different Reynolds numbers (Re) in laminar, transitional, and turbulent flow conditions were obtained. Results indicated that the law of whole change of the skin friction coefficient versus Re is the same for all patterns which can be expressed by an empirical formula C-f = kR(e)(alpha). The model with mixed square and pentagonal patterns always generates the highest skin friction in the different flow conditions, which was speculated to play an important role on the attenuation of the flow separation of the dragonfly wing.