Topographic perturbation of turbulent boundary layers by low-angle, early-stage aeolian dunes
Topographic perturbation of turbulent boundary layers by low-angle, early-stage aeolian dunes
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低角度早期风成沙丘对湍流边界层的地形扰动
DOI：
10.1002/esp.5326
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发表时间：
2022
影响因子：
3.3
通讯作者：
Bristow N
中科院分区：
文献类型：
--
作者：
Bristow N
分米尺度的早期风成底形代表了与成熟沙丘对应物明显不同的地形特征，与成熟沙丘相比，新生形式表现出更平缓的背风坡，其流动平行床剖面呈反向不对称。流动与这些“原沙丘”的发展，其中波峰逐渐向下游转移到其成熟的状态，进行了研究，通过研究扰动的湍流边界层在一系列的代表性的床型。刚性三维模型在折射率匹配的实验水槽中进行了研究，该实验水槽能够在垂直于壁面和平行于壁面的测量平面中使用粒子图像测速技术对平均速度和雷诺应力进行近表面量化。数据表明，强烈的，地形引起的流动扰动的原沙丘，类似的相对程度，发现在成熟的沙丘，尽管他们的低角度的斜坡。波峰的形状被认为是流动扰动发展的一个重要因素，并且只有在波峰最平坦的情况下，流量的最大速度和湍流应力的降低才发生在波峰的上游。对垂直面边界层廓线对数线性的研究表明，尽管廓线受到强烈扰动，但存在对数线性区域，但该区域垂直移动。因此，存在摩擦速度的流向趋势，表现出与平均速度趋势相似的行为。沙丘stoss两侧的内部边界层的增长分析，从脚趾区域开始，揭示了一个类似的发展，所有沙丘的形状，尽管在其脚趾区域的平均速度和湍流应力扰动有明显的差异。本文提供的数据提供了第一个文件的流动形态广泛特征的微妙，低角度，风成原沙丘，并指出关键领域，需要进一步研究，以产生一个更完整的定量理解的流动形式运输耦合，管理他们的形态动力学。
Decimeter‐scale early‐stage aeolian bedforms represent topographic features that differ notably from their mature dune counterparts, with nascent forms exhibiting more gently sloping lee sides and a reverse asymmetry in their flow‐parallel bed profile compared to mature dunes. Flow associated with the development of these “protodunes,” wherein the crest gradually shifts downstream towards its mature state, was investigated by studying the perturbation of the turbulent boundary layer over a succession of representative bedforms. Rigid, three‐dimensional models were studied in a refractive‐index‐matched experimental flume that enabled near‐surface quantification of mean velocities and Reynolds stresses using particle‐image velocimetry in wall‐normal and wall‐parallel measurement planes. Data indicate strong, topographically induced flow perturbations over the protodunes, to a similar relative degree to that found over mature dunes, despite their low‐angled slopes. The shape of the crest is found to be an important factor in the development of flow perturbations, and only in the case with the flattest crest was maximal speed‐up of flow, and reduction in turbulent stresses, found to occur upstream of the crest. Investigation of the log‐linearity of the boundary layer profile over the stoss sides showed that, although the profile is strongly perturbed, a log‐linear region exists, but is shifted vertically. A streamwise trend in friction velocity is thus present, showing a behavior similar to the trends in mean velocity. Analysis of the growth of the internal boundary layer on the dune stoss sides, beginning at the toe region, reveals a similar development for all dune shapes, despite clear differences in mean velocity and turbulent stress perturbations in their toe regions. The data presented herein provide the first documentation of flow over morphologies broadly characteristic of subtle, low‐angle, aeolian protodunes, and indicate key areas where further study is required to yield a more complete quantitative understanding of flow–form–transport couplings that govern their morphodynamics.