Despite two decades of research, drag reduction with superhydrophobic (SHPo) surfaces has never been experimentally confirmed under the most coveted condition, i.e., high Reynolds number flows in open water, thus casting doubt on its ultimate impact. Here, we present large drag reductions (approximately 30%) by SHPo surfaces tested on the sea at ${\mathrm{Re}}_x$ estimated to be as high as $6.5\times {10}^6$. To achieve success, we prepare $4\times 7{\mathrm{cm}}^2$ silicon samples of re-entrant microtrenches for maximum plastron retention and test them as a portion of hull surface underneath a motorboat using a custom-developed comparative shear sensor. The state of plastron on the sample surfaces are observed throughout the tests via a custom-made miniature underwater camera. The successful results attest the importance of microscopic nuances of SHPo surfaces for plastron retention and drag reduction, guiding directions for future applications.

中文翻译：

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超疏水减阻作用在开放水中的湍流

尽管进行了二十多年的研究，但在最令人垂涎​​的条件下（即雷诺数在敞开水中流动的情况下），从未通过实验证实具有超疏水（SHPo）表面的减阻作用，因此对其最终影响产生怀疑。在这里，我们展示了在海上进行测试的SHPo表面的大减阻（大约30％）${\mathrm{回覆}}_X$ 估计高达 $6.5\times {10}^6$。为了取得成功，我们准备$4\times 7{\mathrm{厘米}}^2$可重入的微沟槽的硅样品，可最大程度地保留塑料，并使用定制的比较剪切传感器将其作为摩托艇下方船体表面的一部分进行测试。在整个测试过程中，通过定制的微型水下相机观察样品表面上的的状态。成功的结果证明了SHPo表面的细微差别对于胶保留和减阻的重要性，为将来的应用提供了指导。