Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated shark skin was used as casting template to prepare a flexible female die of silicone rubber by soft die formation. A waterborne epoxy resin was then used to graft long-chains of drag reduction agent and prepare a synthetic drag reduction shark skin with nano-long chain drag reduction interface and lifelike micro-grooves. Replication precision analysis shows that this technology could replicate the complicated three-dimensional morphology of a biological drag reduction surface with high precision. Drag reduction experiments show that the material had an excellent synthetic drag reduction effect, with a maximal drag reduction rate of up to 24.6% over the velocities tested.
It is well known that shark skin surface can effectively inhabit the occurrence of turbulence and reduce the wall friction, but in order to understand the mechanism of drag reduction, one has to solve the problem of the turbulent flow on grooved-scale surface, and in that respect, the direct numerical simulation is an important tool. In this article, based on the real biological shark skin, the model of real shark skin is built through high-accurate scanning and data processing. The turbulent flow on a real shark skin is comprehensively simulated, and based on the simulation, the drag reduction mechanism is discussed. In addition, in order to validate the drag-reducing effect of shark skin surface, actual experiments were carried out in water tunnel, and the experimental results are approximately consistent with the numerical simulation.
On the investigation of biomimetic drag-reducing surface, direct replication of the firm scarfskins on low-resistance creatures to form biomimetic drag-reducing surfaces with relatively vivid morphology relative to the living prototype is a new attempt of the bio-replicated forming technology.Taking shark skin as the bio-replication template, the hot embossing method was applied to the microreplication of its outward morphology. Furthermore, the skins were jointed together to form the drag-reducing surface in large area. The results of the resistance measurements in a water tunnel according to the flat-plate sample pieces have shown that the biomimetic shark-skin coating fabricated by the bio-replicated forming method has significant drag reduction effect, and that the drag reduction efficiency reached 8.25% in the test conditions.
