Sustainability of the plastron on nano-grass-covered micro-trench superhydrophobic surfaces in high-speed flows of open water
Sustainability of the plastron on nano-grass-covered micro-trench superhydrophobic surfaces in high-speed flows of open water
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DOI：
10.1017/jfm.2023.184
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发表时间：
2023-04
影响因子：
3.7
通讯作者：
Ning Yu;Z. R. Li;Alexander McClelland;Francisco Jose del Campo Melchor;Sun Youb Lee;Jae Hwa Lee;C. Kim
中科院分区：
文献类型：
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作者：
Ning Yu;Z. R. Li;Alexander McClelland;Francisco Jose del Campo Melchor;Sun Youb Lee;Jae Hwa Lee;C. Kim
摘要本文研究了由纳米草覆盖的纵向微沟构成的超疏水表面(SHPO)上的地坪的可持续性，主要研究了开阔水域高速流动中的流体动力减阻问题，这代表了普通船舶的工作条件。在修正了剪切驱动排水模型以处理SHPO表面的空气扩散后，结合已有的理论，揭示了浸没深度、空气饱和度和剪应力对最大可达到的粘土层长度的影响趋势。文中还讨论了沟槽两端的动力效应、界面污染和湍流脉动对理论的影响。采用微细加工的方法制作了一系列具有不同沟槽宽度、深度、长度和粗糙度的组合槽面(4 cm×7 cm)，安装在一艘4m长的摩托艇下，在高达7.2m的海水湍流中S−1(剪切率∼83 000 S−1，摩擦雷诺数∼5500)。因为只有当气水界面在海沟顶部被钉住(或仅轻微脱钉)时，Plaston才能提供实质性的滑移，所以使用了两个水下摄像机来区分被钉住(和略被脱钉)的界面和被脱钉(和没有)的界面。除了在6厘米长的沟渠上实现与开放水域中的高速流动对齐的钉扎地块外，实验结果证实了理论估计，支持现场应用的SHPO表面的设计。
Abstract This paper studies the sustainability of plastrons on superhydrophobic (SHPo) surfaces made of longitudinal micro-trenches covered by nano-grass with the main interest on hydrodynamic friction drag reduction in high-speed flows of open water, which represent the operating conditions of common watercraft. After revising the shear-driven drainage model to address the air diffusion for SHPo surfaces, the existing theories are combined to reveal the trends of how the immersion depth, air saturation level and shear stress affect the maximum attainable plastron length. Deviations from the theories by the dynamic effect at the two ends of the trench, the interfacial contaminations and turbulent fluctuation are also discussed. A combinatorial series of well-defined SHPo trench surfaces (4 cm × 7 cm in size with varying trench widths, depths, lengths and roughnesses) is microfabricated and attached underneath a 4 m long motorboat on seawater in turbulent flows up to 7.2 m s−1 (shear rate ∼83 000 s−1 and friction Reynolds number ∼5500). Because the plastron can provide a substantial slip only while its air–water interfaces are pinned (or only slightly depinned) at the trench top, two underwater cameras are employed to differentiate the pinned (and slightly depinned) interfaces from the depinned (and no) interfaces. In addition to achieving pinned plastrons on 6 cm long trenches aligned to high-speed flows in open water, the experimental results corroborate the theoretical estimations, supporting the design of SHPo surfaces for field applications.