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Analysis of Coherent Structures Generated by Plant Stems Using LES

Author(s): Neary Vincent; Constantinescu S. George; Cui Jie

Linked Author(s): George Constantinescu

Keywords: LES; CFD; Turbulence; Vegetation

Abstract: The results from two LES modelling approaches to study fundamental flow physics around simulated plant stems as well as their global effect on the channel flow are presented. In the first approach the focus is on the local flow around isolated or groups of plant stems and the flow is resolved around each of the plant stems. Results from a preliminary simulation corresponding to the LES around an isolated emergent plant stem on a scoured bed with an incoming fully developed turbulent flow are presented to illustrate the capability of this approach. In the second approach the turbulent flow in a channel with a layer of submerged stems is investigated by simply adding a drag force within the entire flow obstructed stem layer region (the so-called diffused drag approach). Both approaches can provide insights on the role of coherent structures on the transport of sediment, nutrients and pollutants in vegetated channel flows. The numerical methods of the two modelling approaches are summarized. The important coherent structures found in vegetated flows are resolved, and their role in momentum and mass transport discussed. However, experimental measurements using advanced techniques, and of sufficient resolution, are not yet available to allow rigorous validation. Although the second approach prohibits resolution of coherent structures around individual plant stems, it nevertheless resolves rib and roller vortices generated by the shear layer instability at the top of the submerged stems and may be the preferred approach if stem densities are high.

DOI:

Year: 2007

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