基于结构仿生的鲨鱼皮微沟槽减阻表面滚压复制理论与方法研究

Nowadays,shark skin is mainly replicated by the planar thermoforming technology. The current technology has some disadvantages, such as long replication cycle, high cost, small area and discontinuous replication. In this project, a novel micro riblets replication method of shark skin by roll-to-roll embossing is proposed. Aimed at the fluid field of micro riblets, the drag-reduction mechanism of shark skin will be discovered by the turbulent boundary layer theory, the combination of Micro-PIV experiment and numerical simulation. The fabrication method of roll-to-roll mold is given by the biological restriction forming, micro electroforming and micro-EDM. The problem of short mold life will be solved by this proposed method. Surface and interface force between mold surface and bionic shark skin will be analyzed. And surface coating technology is used to reduce the surface energy of mold. At the same time, the processing parameters will also be optimized to solve the problem of mold release. The UV-curing method of skin replication is proposed to solve the problem of polymer viscoelastic recovery after roll-to-roll embossing. Based on the micro thermoforming theory, the replication theory and method of the micro riblets drag-reduction surface for shark skin will be established. The research results of the project are very important to develop the non-smooth bionic drag reduction theory and replication technology, to promote its wide application in the field of aircraft, ships and other drag reduction. Therefore，the project has the important scientific significance and practical value.

目前鲨鱼皮复制主要依靠平面热压成型技术，复制周期长、成本高，无法大面积连续复制。为此，本项目首次提出一种鲨鱼皮微沟槽减阻表面滚压复制新方法。以微沟槽区域的流场分布为研究对象，采用湍流边界层理论、Micro-PIV实验和数值模拟相结合的方法，揭示鲨鱼皮微沟槽减阻机理。提出一种生物约束成形、微细电铸和微细电火花相结合的方法，制造鲨鱼皮微沟槽金属滚压模具，解决目前鲨鱼皮树脂模具寿命低的问题。开展模具与仿生鱼皮之间表面和界面力分析，提出采用表面涂层技术来降低模具表面能，同时结合工艺过程优化解决脱模困难问题。提出采用紫外光固化方法复制鲨鱼皮微沟槽，解决滚压后高聚物粘弹性回复问题，结合微热压成型理论，建立基于结构仿生的微沟槽减阻表面滚压复制理论和方法。项目的研究成果对于发展非光滑表面仿生减阻理论及复制技术，推动其在飞行器、舰船等工程减阻领域的广泛应用，都具有重要的科学意义和实际价值。

鲨鱼皮表面微沟槽结构具有优良的减阻性能，在工程减阻领域具有重要的应用前景。但是大面积、高精度、高效率复制出具有较佳减阻效果的仿生鲨鱼皮比较困难。为此，本项目开展了基于结构仿生的鲨鱼皮微沟槽减阻表面的滚压复制技术研究。通过数值模拟，揭示了真实鲨鱼皮微沟槽和鲨鱼皮简化微结构的减阻机理，即沟槽表面大部分区域流动较为平静，大部分区域的剪应力较低；沟槽内部横截面流速波动远小于平面横截面的流速波动，沟槽表面流体的动量转换较为平缓。运用工程优化思想，建立了鲨鱼皮简化微结构和减阻性能之间的构效关系和设计准则。实现了真实鲨鱼皮微沟槽和鲨鱼皮简化微结构到树脂和金属模具的转移复制，即分别采用热压成型、电铸电火花等方法制造出真实鲨鱼皮微沟槽滚压PMMA模具和NAK80模具；采用高速铣削、UV-LIGA技术、钢丝缠绕等方法制造出鲨鱼皮简化微结构的精密滚压模具。建立了真实鲨鱼皮微沟槽在聚合物表面连续滚压成型的有限元模型，揭示了滚压成型过程聚合物基体的温度、压力、应力、应变等分布情况和变化历程。开展了滚压成型工艺实验，在聚合物基体上连续复制出真实鲨鱼皮微沟槽和鲨鱼皮简化微结构，获得了滚压成型工艺参数对微结构复制精度的影响规律，即滚压成型适合在模具温度接近聚合物玻璃转化温度(Tg)、较高的滚压压力以及较低的滚压速度条件下进行。通过对真实鲨鱼皮微沟槽和鲨鱼皮简化微结构表面特性的研究，揭示了沟槽结构参数与沟槽表面疏水性的关系。沟槽结构使液滴和沟槽底部之间存在一部分截留空气，液滴在沟槽表面由固-液接触变为固-液、气-液复合接触，增强了沟槽表面的疏水性，同时提高了微沟槽结构的减阻性能。本项目的研究成果对于发展非光滑表面仿生减阻理论及复制技术，推动其在飞行器、潜航器、舰船等工程减阻领域的广泛应用，都具有重要的科学价值和实际意义。