In this study, particle image velocimetry and electrochemical measurements were applied simultaneously to examine the relationship between wall shear stress and the three-component velocity field in pipe flow. Moreover, the large-scale motions in the velocity field were separated into very-large-scale motions (VLSMs) and large-scale motions (LSMs) to investigate their respective influences on the wall shear stress fluctuations. The conditional velocity field during negative wall shear stress fluctuations confirmed the existence of the “footprints” of the streamwise and wall-normal velocity components in VLSMs. Furthermore, a pair of counter-rotating roll modes was found to appear in VLSMs, which exhibited length scales of _x > 3R, where R is the pipe radius. In contrast, in LSMs, which exhibit length scales of 0.6R …

中文翻译：

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大型结构对管道流动中壁面剪应力波动的影响

在这项研究中，同时应用了颗粒图像测速和电化学测量来检查壁切应力与管道流动中三分量速度场之间的关系。此外，将速度场中的大型运动分为超大型运动（VLSM）和大型运动（LSM），以研究它们各自对壁切应力波动的影响。负壁剪应力波动期间的条件速度场证实了VLSMs中流向和壁法向速度分量的“足迹”的存在。此外，发现在VLSM中出现一对反向旋转的轧辊模式，其长度尺度为_x> 3R，其中R为管道半径。相反，在LSM中，其长度比例为0.6R…