水下复杂形貌固体表面的气层稳定性及流动减阻机理研究

复杂形貌固体表面通常具有从微观到宏观的多级结构，在水下将形成具有多级特征的液气界面，其宏观表现为附着在固体表面的气层。稳定的气层可以形成滑移边界条件，实现复杂流动状态下的减阻，在水下航行、管道输运、生物医学等领域中具有重要应用。同时，固体表面的多级微结构及附近精细流动结构的变化也会对宏观流体特性产生显著影响，具有多尺度特征。本项目拟设计和搭建原位测量液气界面减阻性能的实验平台，以及精细测量边界层流场的高速显微成像系统。针对不同液体压强和复杂流场条件，研究具有多级特征的液气界面的稳定性及演化规律，实现长时间的稳定状态。通过测量流场近壁面精细涡结构和速度分布，探究微观固体表面形貌及流动结构变化对宏观流体特性的影响，揭示具有多级特征的液气界面减阻的内在机理。同时，利用先进的增材制造技术，研制具有良好稳定性和减阻性能的复杂结构固体表面。本项目为实现新型水下运动物体的减阻提供理论指导和设计依据。

Complex solid surfaces usually have hierarchical structures from microscale to macroscale. As these complex structures are immersed underwater, liquid-gas interfaces with multi-level features will form, which performs as a whole gas cushion attached to the solid surface at macroscale. The stable gas cushion can provide slip boundary conditions and realize drag reduction in complex flow conditions, which has significant applications in underwater navigation, pipeline transport, microfluidics, biomedicine and etc. Meanwhile, the hierarchical microstructures on solid surface and the near-wall fine flow structures have significant impacts on the flow field at macroscale, which presents multi-scale characteristics. In this project, we plan to design and build an in situ experimental platform to measure the drag reduction of liquid-gas interfaces, and a high-speed microscopic imaging system to directly observe the fine flow structures in the boundary layer. Stability and evolution of liquid-gas interfaces with multi-scale features will be investigated under different liquid pressures and complex flow conditions in order to achieve a long-term stable state. By measuring the near-wall velocity and fine vortex structures, the influence of the morphology of complex surfaces and flow structures on the macroscopic flow field will be pursued in order to reveal the mechanism of drag reduction due to the multi-level liquid-gas interfaces. At the same time, the design and fabrication of the complex structures on solid surfaces with good stability and drag reduction performances will be carried out by using advanced additive manufacturing technology. This project enables the designs of the new types of underwater vehicles with good performances on drag reduction and efficiency.