【作者】 张硕；

【导师】 李春曦；

【作者基本信息】 华北电力大学 ， 热能工程， 2017， 硕士

【摘要】 近年来,人们受自然界中荷叶、水稻叶和芋头叶等植物表面疏水特性的启发,越来越关注超疏水表面的特性。超疏水表面在减小流动阻力和自清洁材料方面具有良好的应用前景。超疏水表面具有凹凸不平的粗糙微结构,在表面张力作用下,流体流过时并不能完全浸润微结构,而在这些微结构之间驻留部分气体,形成剪切力较小的气-液接触面,极大减少了表面上的固-液接触面积,从而降低流体流过时的粘性阻力。有关超疏水微通道中流动减阻的研究表明,气-液界面曲率对滑移长度和减阻效果具有显著影响。因此,本文着重研究了气-液界面对超疏水微通道中流动减阻的影响,主要内容如下:(1)针对表面具有横向微坑的超疏水微通道中的流动减阻特性,基于抛物线型气-液界面,采用VOF模型对微通道中的单侧滑移流动进行了二维定常数值模拟,研究了层流状态下超疏水微通道中的流动运动学特征,并分析了入口速度、微坑面积比、微通道高度、抛物线型高度、微坑深度和微坑形状对流动减阻的影响。(2)为进一步全面地探讨层流状态下气-液界面曲率对超疏水微通道中流动减阻的影响,定义气-液界面切线与微脊表面所在水平线间的夹角为凸出角?,当?取值范围为-90?~90?时,针对微通道中的双侧滑移流动进行了二维定常数值模拟,并分析了凸出角、自由剪切面积比、微通道高度和雷诺数对减阻效果的影响。更多还原

【Abstract】 In recent years,inspired by hydrophobic property of lotus leaves,rice leaves and taro leaves in nature,people have paid more and more attention to the characteristics of superhydrophobic surfaces,which have good application prospects in reducing the flow resistance and self-cleaning materials.There are rough microstructures in superhydrophobic surfaces,and due to the effect of surface tension,the flowing liquid cannot fully penetrat the cavities in between the microridges and a gas-liquid interface thus forms between two adjacent microridges with air being trapped in the cavities,which greatly reduces the solid-liquid contact area on the surface and thus decreases the viscous resistance of the flowing liquid.The researches on the flow drag reduction in superhydrophobic microchannels show that the gas-liquid interface curvature has significant influence on the slip length and drag reduction effect.Therefore,this paper has emphatically studied the effect of the gas-liquid interface on drag reduction in superhydrophobic microchannels.The main contents of this paper are as follows:(1)For the flow drag reduction characteristics in superhydrophobic microchannels with transverse cavities,the VOF model is employed to simulate the two-dimensional single slip flow in microchannels with given parabolic gas-liquid interfaces.The flow kinematics characteristics in superhydrophobic microchannels are analyzed in the laminar regime,and the effects of the inlet velocity,the cavity fraction,the microchannel height,the parabolic height,the cavity depth and the cavity shape on drag reduction are examined.(2)In order to further investigate the effect of gas-liquid interface curvature on flow drag reduction in superhydrophobic microchannels comprehensively,the angle between the tangent line of the gas-liquid interface and the horizontal line on the surface of the microridge is defined as protrusion angle ?,and the two-dimensional bilateral slip flow in superhydrophobic microchannels is simulated for ?=-90?~90?.The effects of the protrusion angle,the shear-free fraction,the microchannel height and Reynolds number on drag reduction are investigated.更多还原