{"title":"Vortex core regions of nebkhas and their implications on shadow dune formation","authors":"Yongcheng Zhao, Xin Gao, Jiaqiang Lei","doi":"10.1016/j.aeolia.2024.100926","DOIUrl":null,"url":null,"abstract":"<div><p>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 (<em>W</em>) and height (<em>H</em>) of nebkhas, the increment rate decreased massively when the <em>W</em> and <em>H</em> 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 (<em>H/W</em>) 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 <em>H/W</em> < 1. The vortex core region always occurs at the foot of the lee side of nebkhas with the same <em>H/W</em> regardless of the scale of the nebkhas or the incident wind speed.</p></div>","PeriodicalId":49246,"journal":{"name":"Aeolian Research","volume":null,"pages":null},"PeriodicalIF":3.1000,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Aeolian Research","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1875963724000375","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOGRAPHY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
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.
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.