Entrainment of Sediment Particles in Protection Layers

Xerxes Mandviwalla, Erik Damgaard Christensen

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Abstract

Protection layers are often used to prevent scour and erosion, e.g., prevention of scour around wind turbine foundations. However, several cases exist where installed scour protection has settled, where loss of sediment through the armor layer can explain the failure. This paper presents the use of a detailed large eddy simulation–discrete-element method (LES-DEM) model to study sediment particles in porous media. First, a simple idealized case of the removal of sediment from an idealized cavity beneath a smooth turbulent boundary layer was set up. The model showed the penetration of turbulence, mainly in the form of sweep events, into the cavity. This high momentum would at times reach the bottom and entrain the fine sediments. The sediment would subsequently roll over and form a pile and at times be suspended from the return flow of the penetrating turbulence. Finally, a more realistic armor layer was set up with a series of closely packed spheres. Fine sediments were seeded at the bed. A hydraulically rough boundary layer was developed over the armor layer, where turbulent statistics from the model compared well against experiments. Turbulent structures characteristic of the bursting process were identified in the rough wall case. The penetration of sweep events’ entrainment and suspending the finer sediments is detailed. The flushing of cavities from passing ejection events is also presented.
Original languageEnglish
Article number04021040
JournalJournal of Hydraulic Engineering
Volume147
Issue number10
Number of pages14
ISSN0733-9429
DOIs
Publication statusPublished - 2021

Bibliographical note

This material may be downloaded for personal use only. Any other use requires prior permission of the American Society of Civil Engineers. This material may be found at: https://ascelibrary.org/doi/10.1061/%28ASCE%29HY.1943-7900.0001898

Keywords

  • Sediment particles
  • Protection layer
  • Turbulence over roughness elements

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