Abstract
Natural shark skin has a well-demonstrated drag reduction function, which is mainly owing to its microscopic structure and mucus on the body surface. In order to improve drag reduction, it is necessary to integrate microscopic drag reduction structure and drag reduction agent. In this study, two hybrid approaches to synthetically combine vivid shark skin and polymer additive, namely, long-chain grafting and controllable polymer diffusion, were proposed and attempted to mimic such hierarchical topography of shark skin without waste of polymer additive. Grafting mechanism and optimization of diffusion port were investigated to improve the efficiency of the polymer additive. Superior drag reduction effects were validated, and the combined effect was also clarified through comparison between drag reduction experiments.
Highlights
Shark skin effect has attracted worldwide attention over the past few decades because of its superior drag reduction property [1]
It was found that the hierarchical surface morphology with microscopic structure and nano-long-chain mucus was main structural characteristics of shark skin, which results in such amazing drag reduction
Overlying the bioreplicated shark skin with microport array upon a fluid channel layer which is fabricated via microwire mold (Figure 8) is one way to obtain synthetic drag reduction skin based on polymer additive diffusion
Summary
Shark skin effect has attracted worldwide attention over the past few decades because of its superior drag reduction property [1]. The drag reduction rate of microgroove drag reduction surface has not reached 10% in the water tunnel test [3,4,5,6,7] To overcome this drawback, the bioreplication forming process in which real shark skin is directly taken as a template has been attempted for the manufacture of a vivid biomimetic drag reduction surface with a microscopic structure [8, 9]. A positive synthetic effect was demonstrated, almost all drag reduction surfaces were realized via the simple integration of the U/V microgroove with polymer additive, which have several serious problems such as (1) the difficulty in maintaining the groove shape and improvement of drag reduction which is limited by coating; (2) the immense waste of polymer additive by diffusion into whole fluid. The synthetic drag reduction of integrated vivid shark skin with polymer additive is validated by water tunnel test, and synthetic drag reduction mechanism is exploited
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