Direct velocity measurements of the flow past drag-reducing ultrahydrophobic surfaces
Direct velocity measurements of the flow past drag-reducing ultrahydrophobic surfaces
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DOI：
10.1063/1.2109867
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发表时间：
2005-10-01
影响因子：
4.6
通讯作者：
Rothstein, JP
中科院分区：
文献类型：
--
作者：
Ou, J;Rothstein, JP
通过一系列实验研究了减阻超疏水表面的水流运动学。超疏水表面由硅晶片使用光刻法制造，并被设计成包含在流动方向上对齐的微米大小的脊的精确图案。脊通过与有机硅烷的化学反应而变得疏水。一个实验流动池是用来测量的速度分布和压降作为一系列的矩形横截面的微通道几何形状和超疏水表面设计的流速的函数。微通道的速度分布是通过微粒子图像测速（μ-PIV）测量，能够解决流的长度尺度远低于表面特征的大小来确定。通过这些详细的速度测量，它表明，滑动沿着支持之间的疏水微米大小的脊的无剪切空气-水界面是主要的机制，负责观察到的超疏水表面上的流动的阻力减少。超过60%的平均速度在微通道中的最大滑移速度被发现在无剪切空气-水界面的中心，而无滑移边界条件被发现持有沿着表面的疏水脊。实验的速度和压降测量值进行比较，预测的数值模拟和分析理论的基础上的一个简单的模型组成的交替的无剪切和无滑移带的超疏水表面具有良好的协议。(c)2005年美国物理学会。
A series of experiments are presented which study the flow kinematics of water past drag-reducing superhydrophobic surfaces. The ultrahydrophobic surfaces are fabricated from silicon wafers using photolithography and are designed to incorporate precise patterns of micrometer-sized ridges aligned in the flow direction. The ridges are made hydrophobic through a chemical reaction with an organosilane. An experimental flow cell is used to measure the velocity profile and the pressure drop as a function of the flow rate for a series of rectangular cross-section microchannel geometries and ultrahydrophobic surface designs. The velocity profile across the microchannel is determined through microparticle image velocimetry (mu-PIV) measurements capable of resolving the flow down to lengthscales well below the size of the surface features. Through these detailed velocity measurements, it is demonstrated that slip along the shear-free air-water interface supported between the hydrophobic micrometer-sized ridges is the primary mechanism responsible for the drag reduction observed for flows over ultrahydrophobic surfaces. A maximum slip velocity of more than 60% of the average velocity in the microchannel is found at the center of the shear-free air-water interface whereas the no-slip boundary condition is found to hold along the surface of the hydrophobic ridges. The experimental velocity and pressure drop measurements are compared to the predictions of numerical simulations and an analytical theory based on a simple model of an ultrahydrophobic surface composed of alternating shear-free and no-slip bands with good agreement. (c) 2005 American Institute of Physics.