摘要
使用时间分辨的二维粒子图像测速技术(2D-PIV),测量了超疏水壁面(SHS)在槽道中的湍流边界层。基于边界层厚度的摩擦雷诺数在119至173之间。SHS具有微米级的流向沟槽结构,并在展向上均匀分布。实验发现SHS的摩擦系数均小于光滑壁面,且随雷诺数的增加而减少。当摩擦雷诺数约为150并且气体比例分数为0.65时,阻力比存在一个合理的“极小区域”。所有SHS的阻力比均与摩擦雷诺数呈显著负相关关系,并随着无量纲粗糙度宽度的增加而降低。同时还发现无量纲粗糙度宽度等于4为临界位置,此时初始阻力比会随着无量纲粗糙度宽度的增加沿三次多项式迁移。本文通过分析摩擦雷诺数、气体比例分数以及无量纲粗糙度宽度,提出了包含一种新的无量纲特征参数的减阻模型,该模型展示了与摩擦雷诺数、气体比例分数以及无量纲粗糙度宽度有关的函数关系。本研究结果可以加强关于SHS减阻各相关因素之间的联系,同时为微米级结构的设计提供合理的预测和优化方案。
Time-resolved two-dimensional particle images velocimetry(2D-PIV)is used to measure turbulent boundary layer of superhydrophobic surfaces(SHSs)in a channel.The friction Reynolds number based on boundary layer thickness is ranged from 119to 173.The SHSs have spanwiseuniform micro-order grooves in the streamwise direction.All the coefficients of frictions are lower than the counterparts of smooth surface and uniformly exhibit a decrease with the increase of Reynolds number.There is a“minimum region”of drag ratio around gas fraction equating to 0.65at a friction Reynolds number of about 150,which is considered reasonable.A significant negative correlation is observed between drag ratio and all friction Reynolds number.All drag ratios show a significant decrease with the increase of dimensionless roughness width.There is a critical position where the dimensionless roughness width is about 4.The initial drag ratio will migrate along the cubicpolynomial fitting with the increase of dimensionless roughness width,until the corresponding dimensionless roughness width reaches 4.A new dimensionless characteristic parameter is proposed through the analysis of influences on drag ratio of friction Reynolds number,gas fraction and dimensionless roughness width.A model of drag reduction with this dimensionless parameter is proposed as a function of the friction Reynolds number,gas fraction,and dimensionless roughness width.The results of this investigation can strengthen the links between the relevant factors in the drag reduction of the superhydrophobic surfaces and provide reasonable predictions and optimizing solutions in the rational design of the microstructures.
作者
郭新宇
夏振炎
GUO Xinyu;XIA Zhenyan(School of Mechanical Engineering,Tianjin University,Tianjin 300054,China)
出处
《实验力学》
CSCD
北大核心
2023年第3期378-386,共9页
Journal of Experimental Mechanics
基金
国家自然科学基金项目(11372219,51279124)。
关键词
超疏水壁面
粒子图像测速
湍流边界层
减阻
superhydrophobic surfaces
particle images velocimetry
turbulent boundary layer
drag reduction
