The spatial structure of the logarithmic region in very-high-Reynolds-number rough wall turbulent boundary layers
The spatial structure of the logarithmic region in very-high-Reynolds-number rough wall turbulent boundary layers
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DOI：
10.1017/jfm.2018.759
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发表时间：
2018-10-26
影响因子：
3.7
通讯作者：
Guala, Michele
中科院分区：
文献类型：
--
作者：
Heisel, Michael;Dasari, Teja;Guala, Michele
利用超大尺度粒子图像测速技术（SLPIV），研究了雷诺数R-e τ近似于0的全粗糙大气表层近壁区域的空间结构（10(6)）。现场由相对平坦、积雪覆盖的农田组成，允许在接近中性热稳定条件下形成完全粗糙的湍流边界层。成像视场从地面以上3米延伸到19米，并捕获粗糙度子层的顶部和广泛对数区域的底部。SLPIV技术使用天然降雪作为流成像的种子粒子。我们证明了SLPIV在流向和壁法方向上提供了可靠的一阶和二阶速度统计测量。我们在对数区域的结果表明，在实验室研究中确定的结构特征同样存在于大气中。利用瞬时矢量场和两点相关分析，我们识别了具有发夹涡旋包特征的涡旋结构。我们还通过跟踪均匀动量带（umz）和均匀动量带之间的剪切界面在空间和时间上的变化来评价边界层的纬向结构。对剪切界面和剪切界面的统计揭示了纬向结构在确定均数和方差剖面中的作用。剪切界面上的速度差随摩擦速度的变化而变化，与前人的研究结果一致；剪切界面的尺寸随壁法向距离的变化而变化，与附加涡动框架的变化一致。
Using super-large-scale particle image velocimetry (SLPIV), we investigate the spatial structure of the near-wall region in the fully rough atmospheric surface layer with Reynolds number R-e tau similar to O(10(6)). The field site consists of relatively flat, snow-covered farmland, allowing for the development of a fully rough turbulent boundary layer under near-neutral thermal stability conditions. The imaging field of view extends from 3 m to 19 m above the ground and captures the top of the roughness sublayer and the bottom of an extensive logarithmic region. The SLPIV technique uses natural snowfall as seeding particles for the flow imaging. We demonstrate that SLPIV provides reliable measurements of first- and second-order velocity statistics in the streamwise and wall-normal directions. Our results in the logarithmic region show that the structural features identified in laboratory studies are similarly present in the atmosphere. Using instantaneous vector fields and two-point correlation analysis, we identify vortex structures sharing the signature of hairpin vortex packets. We also evaluate the zonal structure of the boundary layer by tracking uniform momentum zones (UMZs) and the shear interfaces between UMZs in space and time. Statistics of the UMZs and shear interfaces reveal the role of the zonal structure in determining the mean and variance profiles. The velocity difference across the shear interfaces scales with the friction velocity, in agreement with previous studies, and the size of the UMZs scales with wall-normal distance, in agreement with the attached eddy framework.