Investigation of the drag reducing effect of hydrophobized sand on cylinders
Investigation of the drag reducing effect of hydrophobized sand on cylinders
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DOI：
10.1088/0022-3727/47/20/205302
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发表时间：
2014-05-21
影响因子：
3.4
通讯作者：
Newton, M. I.
中科院分区：
文献类型：
--
作者：
Brennan, J. C.;Fairhurst, D. J.;Newton, M. I.
超疏水表面显示出强大的减阻应用潜力。如果这种表面支持低固体表面分数的Cassie-Baxter状态，并且在浸入时保留板层空气层，则其表面可能发生大滑移，从而减少阻力。在这项工作中，我们报告了一种简便的方法，用于创建具有不同表面粗糙度的疏水圆柱体和疏水平面，能够支持Cassie-Baxter状态。在直径为12mm的圆柱体上涂覆50- 100,212 - 300,425 -600和600-710 μ m的疏水性砂，以产生不同程度的粗糙度。用激光多普勒风速仪在大型水循环流室中测量了水在尾迹上的速度分布。对于雷诺数在10000到40000之间的流动，Cassie-Baxter状态下的疏水圆柱体与Wenzel状态下的相同样品相比，阻力减少了28%。这些减阻结果，结合板层空气层和特征高度的共聚焦显微镜图像，表明板层的厚度和特征的突出高度结合在一起，根据两者的比例产生减阻或增阻。
Superhydrophobic surfaces show strong potential for drag reducing applications. If such a surface supports a Cassie-Baxter state with low solid surface fraction and when immersed it retains a plastron air layer, large slip can occur across its surface as well as a consequent reduction in drag. In this work we report a facile method for creating hydrophobic cylinders and hydrophobic flat surfaces with varying surface roughness able to support a Cassie-Baxter state. Cylinders of 12mm diameter were coated in hydrophobized sand with grain sizes in the ranges of 50-100, 212-300, 425-600 and 600-710 mu m to produce the varying degrees of roughness. A laser Doppler anemometer was used to measure the velocity profile of the water across their wake in a large water circulating flow chamber. The hydrophobic cylinders in the Cassie-Baxter state show drag reductions of up to 28% compared to the same sample in the Wenzel state for flows with Reynolds numbers of 10000 to 40000. These drag reduction results, in combination with confocal microscopy images of the plastron air layer and feature height, show that the thickness of the plastron and the protrusion height of the features combine to give a drag reduction or drag increase depending on the ratio of the two.