Large Eddy Simulation of three-dimensional flow structures over wave-generated ripples

Chuang Jin, Giovanni Coco, Rafael O. Tinoco, Pallav Ranjan, Jorge San Juan, Som Dutta, Heide Friedrich, Zheng Gong

Research output: Contribution to journalArticlepeer-review

Abstract

We performed a three-dimensional high-resolution Large Eddy Simulation using a sinusoidal ripple-like bedform geometry with spacing and amplitude consistent with equilibrium conditions under the prescribed oscillatory forcing. The simulation results are validated qualitatively and quantitatively with previous laboratory experiments and numerical simulations. Our numerical simulations allow to analyze the presence of “ribs”, strong flow rotational features in the spanwise direction developing perpendicular to the ripple crest. We show that ribs tend to appear on the upslope and crest of ripples and display a dominant spacing, ranging from 0.5λ to λ, during wave phases associated to flow acceleration. When the vortex is transported over the downstream ripple during the flow deceleration, ribs appear for the second time over the upslope of the downstream ripple, with the dominant spacing about 1/8 ripple wavelength. The presence of flow three-dimensionality corresponds to a large variability of the shear stress over ripples in the spanwise direction, which could ultimately favor the development of three-dimensional geometry. The three-dimensional vortex dynamics are evaluated using the concept of vortex strength. Peak vortex strength is observed at the maximum free stream velocity, but the largest variation of the vortex strength and vortex size in the spanwise direction occurs prior to the flow reversal. The variability of the vortex structures might provide a favorable setting for the development of ribs and might relate to the spacing of ribs.

Original languageEnglish (US)
Pages (from-to)1536-1548
Number of pages13
JournalEarth Surface Processes and Landforms
Volume46
Issue number8
DOIs
StatePublished - Jun 30 2021
Externally publishedYes

Keywords

  • Large Eddy Simulation
  • oscillatory flow
  • ribs
  • ripples
  • vortex

ASJC Scopus subject areas

  • Geography, Planning and Development
  • Earth-Surface Processes
  • Earth and Planetary Sciences (miscellaneous)

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