Superhydrophobic drag reduction in high-speed towing tank
Superhydrophobic drag reduction in high-speed towing tank
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DOI：
10.1017/jfm.2020.872
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发表时间：
2020-12
影响因子：
3.7
通讯作者：
Muchen Xu;N. Yu;John Kim;C. Kim
中科院分区：
文献类型：
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作者：
Muchen Xu;N. Yu;John Kim;C. Kim
摘要 只要腹甲持续存在，超疏水（SHPo）表面有望减少任何流动条件下的表面摩擦阻力，包括海洋船舶的大规模湍流边界层流。然而，尽管使用实验室设施成功地减少了阻力，但 SHPo 表面的腹甲在开放水域的高雷诺数流中持续丢失，并且直到最近使用船下的某些微沟槽 SHPo 表面进行的研究才报告有减阻（Xu 等人，Phys. Rev. Appl.，第 13 卷，第 3 期，2020，034056）。由于对海水上的船进行受控流动的科学研究很困难，因此在本文中，我们通过开发一种新颖的 $0.7\ \textrm {m} \times 1.4\ \textrm {m}$ 拖板，在高速拖曳池中测试类似的 SHPo 表面，该拖曳池提供良好控制的开放水域流，该拖盘将 $4\ \textrm {cm} \times 7\ \textrm {cm}$ 样本置于高雷诺数流中。板。除了 7 厘米长的微沟槽外，还测试了长度分为两部分的沟槽，并显示出改进。发现相对于光滑表面的表面摩擦阻力比随着雷诺数的增加而减小，在 $Re_x\sim 8\times 10^6$ 时降至 73%（即 27% 阻力减少），然后开始以更高的速度增加。对于给定的气体分数，发现无量纲到粘性长度尺度的沟槽宽度控制减阻，这与之前的数值结果一致。
Abstract As far as plastron is sustained, superhydrophobic (SHPo) surfaces are expected to reduce skin-friction drag in any flow conditions including large-scale turbulent boundary-layer flows of marine vessels. However, despite many successful drag reductions reported using laboratory facilities, the plastron on SHPo surfaces was persistently lost in high-Reynolds-number flows on open water, and no reduction has been reported until a recent study using certain microtrench SHPo surfaces underneath a boat (Xu et al., Phys. Rev. Appl., vol. 13, no. 3, 2020, 034056). Since scientific studies with controlled flows are difficult with a boat on ocean water, in this paper we test similar SHPo surfaces in a high-speed towing tank, which provides well-controlled open-water flows, by developing a novel $0.7\ \textrm {m} \times 1.4\ \textrm {m}$ towing plate, which subjects a $4\ \textrm {cm} \times 7\ \textrm {cm}$ sample to the high-Reynolds-number flows of the plate. In addition to the 7 cm long microtrenches, trenches divided into two in length are also tested and reveal an improvement. The skin-friction drag ratio relative to a smooth surface is found to be decreasing with increasing Reynolds number, down to 73 % (i.e. 27 % drag reduction) at $Re_x\sim 8\times 10^6$, before starting to increase at higher speeds. For a given gas fraction, the trench width non-dimensionalized to the viscous length scale is found to govern the drag reduction, in agreement with previous numerical results.