表面微纳结构对气-水界面稳定性和流动减阻的影响

利用压力-流量测量和流动显示方法研究了6种具有不同微纳结构尺寸的超疏水表面的减阻效果以及表面微结构形状对气-水界面稳定性的影响。实验结果表明:设计的各种超疏水表面在层流和湍流下均具有一定的减阻效果；在相同的固体面积分数情况下，微结构间距越小，减阻效果越好；在具有最小结构间距的微纳二级结构表面上实现了最大减阻率（38.6±4.5）%。流动显示观测发现:减阻率与微结构的层级、尺寸、形貌及槽道流态有关，它们均对气-水界面稳定性有一定的影响，揭示了复合微纳结构之所以能够显著提升减阻效果，是由于添加纳米二级结构减小了原有表面的固体面积分数，并提高了气-水界面的稳定性。此外，对于具有双内凹（伞状）微结构表面的微槽道，即使表面为亲水材料，也可以有效捕捉气体，形成稳定的气-水界面，从而实现超疏水性能。

Effect of surface micro/nano-structure on gas-water interface stability and flow drag reduction

The pressure-flow measurement method and flow visualization are used to study the drag reduction effect of 6 types of super-hydrophobic surfaces with different micro/nano-structure dimensions and the influence of the surface microstructure shape on the gas-water interface stability. The experimental results show that the various superhydrophobic surfaces have a certain drag reduction under laminar flow and turbulent flow conditions. At the same solid area fraction, the smaller the microstructure spacing is, the better the drag reduction effect is. The maximum drag reduction rate, which is (38.6±4.5)%, is achieved on the micro/nano hierarchical structure surface with the smallest structural spacing. The visualization experiment also found that the drag reduction rate is related to the microstructure level, microstructure size, channel flow pattern and microstructure morphology, which all have certain influence on the gas-water interface stability. The hierarchical micro/nano-structure can significantly improve the drag reduction, because the addition of the nano-secondary structure reduces the solid area fraction of the surface and improves the stability of the gas-water interface. In addition, a microchannel surface with doubly reentrant structures (umbrella structure), even though made of wettable material, can capture and sustain the air-water interface, thereby achieving superhydrophobic performance.