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Instantaneous Transport of a Passive Scalar in a Turbulent Separated Flow

Ouro, P; Fraga, B; Viti, N; Angeloudis, A; Stoesser, T; Gualtieri, C; (2017) Instantaneous Transport of a Passive Scalar in a Turbulent Separated Flow. Environmental Fluid Mechanics , 18 (2) pp. 487-513. 10.1007/s10652-017-9567-3. Green open access

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Abstract

The results of large-eddy simulations of flow and transient solute transport over a backward facing step and through a 180° bend are presented. The simulations are validated successfully in terms of hydrodynamics and tracer transport with experimental velocity data and measured residence time distribution curves confirming the accuracy of the method. The hydrodynamics are characterised by flow separation and subsequent recirculation in vertical and horizontal directions and the solute dispersion process is a direct response to the significant unsteadiness and turbulence in the flow. The turbulence in the system is analysed and quantified in terms of power density spectra and covariance of velocity fluctuations. The injection of an instantaneous passive tracer and its dispersion through the system is simulated. Large-eddy simulations enable the resolution of the instantaneous flow field and it is demonstrated that the instabilities of intermittent large-scale structures play a distinguished role in the solute transport. The advection and diffusion of the scalar is governed by the severe unsteadiness of the flow and this is visualised and quantified. The analysis of the scalar mass transport budget quantifies the mechanisms controlling the turbulent mixing and reveals that the mass flux is dominated by advection.

Type: Article
Title: Instantaneous Transport of a Passive Scalar in a Turbulent Separated Flow
Open access status: An open access version is available from UCL Discovery
DOI: 10.1007/s10652-017-9567-3
Publisher version: https://doi.org/10.1007/s10652-017-9567-3
Language: English
Additional information: This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Keywords: Large eddy simulation, Separation flows, Solute dispersion, Backward facing step, Turbulence
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Civil, Environ and Geomatic Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10058277
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