Influence of surface roughness of dune bedforms on flow and turbulence characteristics

Veysel Sadan Ozgur Kirca*, Seyed Mahdi Saghebian, Kiyoumars Roushangar, Oral Yagci

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

The current paper investigates the flow and turbulence characteristics over dune bedforms by means of laboratory experiments, where spatially dense and temporally high frequency velocity measurements were done. Although similar studies are available in the literature, the focus and novelty of the current study is to assess the influence of surface roughness of the dune bedforms on the nearbed flow. For direct comparison, two different surface roughness heights over idealized, fixed-shaped, high-angled dune bedforms were tested; one with a hydraulically-smooth surface, and the other with a fully-rough surface. Spatial variation of time-averaged flow as well as turbulence statistics were examined, which was complemented by streamline plots and spectral analyses. The results are interpreted from sediment entrainment and sediment transport points of view. The results show that increased dune surface roughness reduces the nearbed flow velocity, but increases the flow velocities at upper regions. The upward directed flow near the dune crests becomes stronger in the case of smooth surface, while the re-attachment point moves further downstream compared to the rough wall case. It is concluded that the roughness of the dune surface affects the nearbed flow and turbulence characteristics qualitatively and quantitatively, which is shown to have direct consequences on sediment entrainment characteristics.

Original languageEnglish
Pages (from-to)666-678
Number of pages13
JournalInternational Journal of Sediment Research
Volume35
Issue number6
DOIs
Publication statusPublished - Dec 2020

Bibliographical note

Publisher Copyright:
© 2020 International Research and Training Centre on Erosion and Sedimentation / the World Association for Sedimentation and Erosion Research

Keywords

  • Bedforms
  • Dunes
  • Form drag
  • Friction drag
  • Grain roughness
  • Turbulence

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