Effect of large-scale structures on wall shear stress fluctuations in pipe flow
Effect of large-scale structures on wall shear stress fluctuations in pipe flow
复制标题
大型结构对管流壁面剪应力脉动的影响
DOI：
10.1103/physrevfluids.5.104601
复制
发表时间：
2020
影响因子：
2.7
通讯作者：
Tsuji Yoshiyuki
中科院分区：
文献类型：
--
作者：
Tong Tong;Bhatt Kovid;Tsuneyoshi Tatsuya;Tsuji Yoshiyuki
本文采用粒子图像测速仪和电化学测量相结合的方法，研究了管流中壁面剪应力与三分量速度场之间的关系。此外，将速度场中的大尺度运动分为超大尺度运动(VLSM)和大尺度运动(LSM)，研究了它们对壁面剪应力波动的影响。壁面剪应力负波动时的条件速度场证实了VLSM中流向速度分量和壁法向速度分量的“足迹”的存在。此外，还发现在VLSM中出现了一对反向旋转的滚转模式，其长度尺度为流向波长和管道半径。相反，在LSM中，没有观察到反向旋转的涡对。本文发现管流中产生对旋涡对的长度-尺度阈值为。这个阈值高于报道的湍流边界层的值，也就是边界层厚度。与平面内条件展向速度相关的壁面剪应力的两点关联式揭示了展向曲折特征对近壁区的影响。
In this paper, 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. Further, a pair of counter-rotating roll modes was found to appear in the VLSMs, exhibiting length scales of, whereis the streamwise wavelength andis the pipe radius. In contrast, in LSMs, which exhibit length scales of, counter-rotating vortex pairs were not observed. In this paper, the length-scale threshold for generating counter-rotating vortex pairs in pipe flow was found to be. This threshold value is higher than the value reported for turbulent boundary layers, which is, whereis the boundary-layer thickness. Two-point correlations of wall shear stress, which are associated with the conditional spanwise velocity in theplane, revealed the effect of spanwise meandering features on the near-wall region.