Experimental study on dominant vortex structures in near-wall region of turbulent boundary layer based on tomographic particle image velocimetry
Experimental study on dominant vortex structures in near-wall region of turbulent boundary layer based on tomographic particle image velocimetry
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DOI：
10.1017/jfm.2019.412
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发表时间：
2019-07
影响因子：
3.7
通讯作者：
Chengyue Wang;Q. Gao;Jinjun Wang;Biao Wang;C. Pan
中科院分区：
文献类型：
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作者：
Chengyue Wang;Q. Gao;Jinjun Wang;Biao Wang;C. Pan
涡结构是湍流边界层中非常重要的研究对象。本文对雷诺数Re_{\unicode [STIX]{x1 D 70 F}}=1238$、2286和3081时的近壁区（$y<0.1\unicode [STIX]{x1 D 6 FF}$）进行了层析粒子图像测速测量。主要的注意力是支付的涡的几何形状和拓扑结构的壁正常的演变。用旋涡强度（$\unicode[STIX]{x1 D 706}_{ci}$）来识别旋涡，用速度梯度张量的真实的特征向量来识别旋涡的方向。研究了流向壁面法向平面和流向展向平面内的涡倾角随壁面法向位置的变化规律，为推测TBL内涡管的三维形状提供了有用的信息。从涡量控制方程出发，讨论了涡量和旋流方向的区别，揭示了它们之间的内在联系。线性随机估计（LSE）被进一步部署到直接提取三维涡模型。喷射事件发生在不同的壁面法线位置的LSE速度场揭示了主导喷射事件的涡的拓扑结构的演变。LSE基于一个中心的展向涡提供了一个典型的数据包模型，这表明在TBL的数据包的人口密度是足够大的有条件的平均流场中留下足迹。这一工作有助于解决关于包结构存在性的激烈争论，也为TBL模型理论奠定了一定的基础。
Vortex structures are very popular research objects in turbulent boundary layers (TBLs) because of their prime importance in turbulence modelling. This work performs a tomographic particle image velocimetry measurement on the near-wall region ( $y<0.1\unicode[STIX]{x1D6FF}$ ) of TBLs at three Reynolds numbers $Re_{\unicode[STIX]{x1D70F}}=1238$ , 2286 and 3081. The main attention is paid to the wall-normal evolution of the vortex geometries and topologies. The vortex is identified with swirl strength ( $\unicode[STIX]{x1D706}_{ci}$ ), and its orientation is recognized by using the real eigenvector of the velocity gradient tensor. The vortex inclination angles in the streamwise–wall-normal plane and in the streamwise–spanwise plane as functions of wall-normal positions are investigated, which provide useful information to speculate on the three-dimensional shape of the vortex tubes in a TBL. The difference between the orientations of vorticity and swirl is discussed and their inherent relationship is revealed based on the governing equation of vorticity. Linear stochastic estimation (LSE) is further deployed to directly extract three-dimensional vortex models. The LSE velocity fields for ejection events happening at different wall-normal positions shed light on the evolution of the topologies for the vortices dominating ejection events. LSE based on a centred prograde spanwise vortex provides a typical packet model, which indicates that the population density of the packets in a TBL is large enough to leave footprints in conditionally averaged flow fields. This work should help to settle the severe debate on the existence of packet structures and also lays some foundation for the TBL model theory.