Abstract The local slip behavior and flow fields near the gas-liquid interface (GLI) of a Newtonian liquid flowing past a superhydrophobic surface with periodic rectangular grooves are investigated using molecular dynamics (MD) simulations. The saturated vapor of the liquid fills the groove to form the GLI. A flat GLI is introduced by carefully adjusting the channel height to make the liquid bulk pressure equal to the coexistence pressure. The setup with the flat GLI allows for an accurate determination of the local slip velocity, shear rate and slip length. We find that the local slip velocity and shear rate at the GLI are well described by the elliptical and exponential functions, respectively. By directly computing the local slip length from the local flow fields, we propose a novel distribution function for the slip length along the GLI for both transverse and longitudinal flows. Moreover, we demonstrate that the relationship between the local and the effective slip lengths in the transverse and longitudinal cases deviates from the continuum assumptions as the groove width is reduced to the nanoscale dimensions. The functional form for the local slip length can be potentially used as a boundary condition in the continuum analysis without considering the explicitly gas flow in the grooves of superhydrophobic surfaces.

中文翻译：

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纳米结构超疏水表面的局部滑移长度和流场

摘要 使用分子动力学 (MD) 模拟研究流过具有周期性矩形凹槽的超疏水表面的牛顿液体的气液界面 (GLI) 附近的局部滑移行为和流场。液体的饱和蒸气填充凹槽以形成 GLI。通过仔细调整通道高度使液体体积压力等于共存压力来引入平坦的 GLI。带有平坦 GLI 的设置允许准确确定局部滑动速度、剪切速率和滑动长度。我们发现 GLI 处的局部滑移速度和剪切速率分别由椭圆函数和指数函数很好地描述。通过直接从局部流场计算局部滑移长度，我们为横向和纵向流动沿 GLI 的滑移长度提出了一种新的分布函数。此外，我们证明了横向和纵向情况下局部滑移长度和有效滑移长度之间的关系偏离了连续假设，因为凹槽宽度减小到纳米级尺寸。局部滑移长度的函数形式可以潜在地用作连续介质分析中的边界条件，而无需考虑超疏水表面凹槽中的明确气流。