Large eddy simulation of shear flow in open channel with emergent or submerged vegetation

Chi Wai Li, X. H. Su

Research output: Chapter in book / Conference proceedingConference article published in proceeding or bookAcademic researchpeer-review

Abstract

Vegetation in open channels will improve the water quality there and provide favorable space for various lives, but it will reduce the flow carrying capacity of the channel by introducing additional resistance to the flow. A Large Eddy Simulation (LES) model has been developed to study the mean flow and turbulence in open channel with vegetation. In the model the vegetation domain is represented by a drag force layer. One equation model is used for subgrid scale turbulence closure. The length scale of turbulence l is proportional to the grid size and the turbulence energy k is obtained from the solution of the turbulence energy transport equation. The model has been applied to simulate cases of open channel flow with emergent or submerged vegetation. For emergent vegetation occupied in a part of an open channel, transverse shear is produced by vegetation drag. Organized large eddies are developed at the interface between the vegetated and non-vegetated regions and the organized flow structure clearly has a life cycle. At the interface the transverse velocity profile exhibits a steep gradient, which induces significant mass and momentum exchange, acts as a source of vorticity, and generates high Reynolds stresses. For submerged vegetation in open channel, the flow near the top of vegetation is unstable and rolls up into discrete vortices. The turbulent intensity and the Reynolds stresses are the strongest there. Interaction of vortices results in a shear layer above the top of vegetation. The agreement between the numerical results and the available experimental data is satisfactory. The present model is a useful tool for further study of turbulent flow with vegetation, as well as for certain engineering applications.
Original languageEnglish
Title of host publicationProceedings of the 2003 - 17th National Conference on Hydrodynamics and the 16th National Congress on Hydrodynamics
Pages18-28
Number of pages11
Publication statusPublished - 1 Dec 2003
EventProceeding of the 2003 17th National Conference on Hydrodynamics and the 6th National Congress on Hydrodynamics - Hong Kong, Hong Kong
Duration: 29 Dec 20034 Jan 2004

Conference

ConferenceProceeding of the 2003 17th National Conference on Hydrodynamics and the 6th National Congress on Hydrodynamics
Country/TerritoryHong Kong
CityHong Kong
Period29/12/034/01/04

Keywords

  • LES
  • Open channel
  • Turbulent flow
  • Vegetation

ASJC Scopus subject areas

  • Engineering(all)

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