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Estimating Stem-Scale Mixing Coefficients in Low Velocity Flows

Author(s): F. Sonnenwald; I. Guymer; A. Marchant; N. Wilson; M. Golzar; V. Stovin

Linked Author(s): Fred Sonnenwald, Ian Guymer

Keywords: No keywords

Abstract: Stormwater ponds are Su DS devices intended to moderate the negative environmental impacts of stormwater run-off. A current, joint, research programme is investigating the effects of heterogeneous vegetation distributions in stormwater ponds and developing Computational Fluid Dynamics (CFD) techniques to simulate3D solute transport processes in low velocity flows. The aim of the project is to generate a unique dataset that describes the influence of different types and configurations of vegetation on the pond’s fundamental flow–and treatment–characteristics. This characterisation can then be used to evaluate existing run-off treatment ponds that may be delivering sub-optimal levels of treatment. This paper presents results from an initial laboratory study, with regular uniform emergent artificial vegetation, from which longitudinal dispersion coefficients have been obtained over a range of target flow velocities in a narrow (Armfield) flume. These have been integrated with stem-scale CFD derived estimates of transverse variation of mean longitudinal velocity across a vegetation cell to investigate the ability of a Chikwendu (1986) n-zone type approach to predict transverse dispersion coefficients over a scale suitable for inclusion in future 3D CFD pond models. Assuming that the small stem-scale variations in velocity form a repeating pattern at the patch scale, and that stem-scale transverse dispersion effects integrate, this approach has been successfully applied to predict transverse and longitudinal mixing in a wide flume solely with longitudinal parameters estimated from a narrow flume.

DOI:

Year: 2016

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