Wall-Shear-Stress-Based Conditional Sampling Analysis of Coherent Structures in a Turbulent Boundary Layer
Wall-Shear-Stress-Based Conditional Sampling Analysis of Coherent Structures in a Turbulent Boundary Layer
复制标题
DOI：
10.1115/1.4049403
复制
发表时间：
2021-04
影响因子：
2
通讯作者：
Sangjin Ryu;Ethan A. Davis;J. S. Park;Haipeng Zhang;J. Yoo
中科院分区：
文献类型：
--
作者：
Sangjin Ryu;Ethan A. Davis;J. S. Park;Haipeng Zhang;J. Yoo
相干结构对湍流边界层的控制至关重要，因为它们在流动中的动量和热量传递中起着重要作用。湍流相干结构可以通过测量作为相干结构足迹的壁面剪应力来检测。在本研究中，使用两个自制的沿展向排列的壁面剪应力探头同时测量了零压力梯度湍流边界层中的壁面剪应力波动。壁面剪应力探头由两根安装在壁面上的热线排成v形排列，用于测量流向和展向剪应力，其性能与直接数值模拟结果进行了对比验证。利用条件采样技术分析了实测壁面剪应力波动与流向速度波动之间的关系。峰值检测方法和变间隔时间平均（VITA）方法表明准流向涡向流向倾斜。当两个探测器同时探测到事件时，探测到更强的流向速度波动，这表明探测到更强的相干结构。与前两种方法相比，休眠事件检测方法检测具有下壁剪应力波动的事件。与壁面规律相比，冬眠事件的整体平均平均速度剖面向上移动，表明与冬眠事件相关的相干结构处于低阻力状态。这些方法表明壁面剪切应力波动与相干结构之间存在显著相关性，可以激励流动控制策略充分利用这些相关性。
Coherent structures are critical for controlling turbulent boundary layers due to their roles in momentum and heat transfer in the flow. Turbulent coherent structures can be detected by measuring wall shear stresses that are footprints of coherent structures. In this study, wall shear stress fluctuations were measured simultaneously in a zero pressure gradient turbulent boundary layer using two house-made wall shear stress probes aligned in the spanwise direction. The wall shear stress probe consisted of two hot-wires on the wall aligned in a V-shaped configuration for measuring streamwise and spanwise shear stresses, and their performance was validated in comparison with a direct numerical simulation result. Relationships between measured wall shear stress fluctuations and streamwise velocity fluctuations were analyzed using conditional sampling techniques. The peak detection method and the variable-interval time-averaging (VITA) method showed that quasi-streamwise vortices were inclined toward the streamwise direction. When events were simultaneously detected by the two probes, stronger fluctuations in streamwise velocity were detected, which suggests that stronger coherent structures were detected. In contrast to the former two methods, the hibernating event detection method detects events with lower wall shear stress fluctuations. The ensemble-averaged mean velocity profile of hibernating events was shifted upward compared to the law of the wall, which suggests low drag status of the coherent structures related with hibernating events. These methods suggest significant correlations between wall shear stress fluctuations and coherent structures, which could motivate flow control strategies to fully exploit these correlations.