Vortex core regions of nebkhas and their implications on shadow dune formation

IF 3.1 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Aeolian Research Pub Date : 2024-04-30 DOI:10.1016/j.aeolia.2024.100926
Yongcheng Zhao, Xin Gao, Jiaqiang Lei
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Abstract

Shadow dunes develop at the lee side of obstacles and are scale-dependent on the obstacle size. However, our recent field investigations showed that the lengths of shadow dunes are not always proportional to the size of obstacles. In this work, field investigations and computational fluid dynamics (CFD) simulations were conducted to study the effects of the scale and vortex of nebkhas on shadow dune development. Results show that although the shadow dune lengths are proportionate to the width (W) and height (H) of nebkhas, the increment rate decreased massively when the W and H of nebkhas are larger than 6 and 2 m, respectively. The CFD simulations suggest that the vortex core regions of the paired symmetrical reversing flow gradually move to the upwind region as the aspect ratio (H/W) of the nebkhas decreases. The size of the paired symmetrical reversing flows is reduced, and the merging of the reversing flows is prevented, potentially entraining the sediments far from the wake region. The sediments could rotate and deposit on both sides of the leeward face of the nebkhas and therefore contribute to the occurrence of short, tongue-like shadow dunes, which are particularly notable when H/W < 1. The vortex core region always occurs at the foot of the lee side of nebkhas with the same H/W regardless of the scale of the nebkhas or the incident wind speed.

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星云涡旋核心区及其对阴影沙丘形成的影响
阴影沙丘在障碍物的背风面形成,与障碍物的大小有关。然而,我们最近的实地调查表明,影丘的长度并不总是与障碍物的大小成正比。在这项工作中,我们进行了实地调查和计算流体动力学(CFD)模拟,以研究nebkhas的规模和涡流对影子沙丘发展的影响。结果表明,虽然阴影沙丘的长度与nebkhas的宽度(W)和高度(H)成正比,但当nebkhas的宽度和高度分别大于6米和2米时,阴影沙丘的增量率会大幅下降。CFD 模拟结果表明,随着星云长宽比(H/W)的减小,成对对称逆转流的涡核区域逐渐向上风区域移动。成对对称逆向流的规模减小,逆向流的合并受到阻碍,可能会将沉积物夹带到远离尾流区域的地方。沉积物可能会旋转并沉积在星云背风面的两侧,从而导致短舌状阴影沙丘的出现,当 H/W < 1 时尤为明显。无论星云的规模或入射风速如何,涡核区总是出现在具有相同 H/W 的星云背风面的底部。
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来源期刊
Aeolian Research
Aeolian Research GEOGRAPHY, PHYSICAL-
CiteScore
7.10
自引率
6.10%
发文量
43
审稿时长
>12 weeks
期刊介绍: The scope of Aeolian Research includes the following topics: • Fundamental Aeolian processes, including sand and dust entrainment, transport and deposition of sediment • Modeling and field studies of Aeolian processes • Instrumentation/measurement in the field and lab • Practical applications including environmental impacts and erosion control • Aeolian landforms, geomorphology and paleoenvironments • Dust-atmosphere/cloud interactions.
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