Time-averaged velocity and scalar fields of the flow over and around a group of cylinders: a model experiment for canopy flows
Time-averaged velocity and scalar fields of the flow over and around a group of cylinders: a model experiment for canopy flows
We conduct a well-controlled model experiment for a wide variety of canopy flows. Examples of these include engineering flows such as wind flow, dispersion of scalars through and over urban areas, and the convective heat transfer in many heat exchangers, as well as natural canopies such as flows through terrestrial or aquatic vegetation. We aim to shed the light on fundamental flow and transport phenomena common to these applications. Specifically, the characteristics of mean flow and scalar concentration characteristics of a turbulent boundary layer flow impinging on a canopy, which comprises a cluster of tall obstacles (this can also be interpreted as a porous obstruction). The cluster is created with a group of cylinders of diameter d and height h arranged in a circular patch of diameter D . The solidity of the patch/obstruction is defined by ϕ (the total planar area covered by cylinders), which is systematically varied ( 0.098≤ϕ≤1 ) by increasing the number of cylinders in a patch ( Nc ). A point source is placed at ground level upstream of the patch and its transport over and around the patch is examined. Time-averaged velocity and scalar fields, obtained from simultaneous planar particle image velocimetry-planar laser-induced fluorescence (PIV-PLIF) measurements, reveal that the characteristics of wake and flow above porous patches are heavily influenced by ϕ . In particular, we observe that the horizontal and vertical extent of the wake and scalar concentration downstream of the patches decreases and increases with ϕ , respectively. Here, the recirculation bubble is shifted closer to the trailing edge (TE) of the patches as ϕ increases, limiting the flow from convecting downstream, decreasing the scalar concentration and virtually ‘extending’ the patch in the streamwise direction. As the bubble forms in the TE, vertical bleeding increases and hence the concentration increases above the patch where the cylinders appear to ‘extend’ vertically towards the freestream.
Mixing and dispersion, Mixing enhancement, Turbulence control, Turbulent boundary layers, Urban fluid dynamics, Wakes
Wangsawijaya, Dea Daniella
b9f307f6-2828-416f-bc41-a025ecf49098
Nicolai, Claudia
8bdc34da-efe2-4dd0-b3bc-ece3bbddebff
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
23 March 2022
Wangsawijaya, Dea Daniella
b9f307f6-2828-416f-bc41-a025ecf49098
Nicolai, Claudia
8bdc34da-efe2-4dd0-b3bc-ece3bbddebff
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Wangsawijaya, Dea Daniella, Nicolai, Claudia and Ganapathisubramani, Bharathram
(2022)
Time-averaged velocity and scalar fields of the flow over and around a group of cylinders: a model experiment for canopy flows.
Flow, 2, [E9].
(doi:10.1017/flo.2022.2).
Abstract
We conduct a well-controlled model experiment for a wide variety of canopy flows. Examples of these include engineering flows such as wind flow, dispersion of scalars through and over urban areas, and the convective heat transfer in many heat exchangers, as well as natural canopies such as flows through terrestrial or aquatic vegetation. We aim to shed the light on fundamental flow and transport phenomena common to these applications. Specifically, the characteristics of mean flow and scalar concentration characteristics of a turbulent boundary layer flow impinging on a canopy, which comprises a cluster of tall obstacles (this can also be interpreted as a porous obstruction). The cluster is created with a group of cylinders of diameter d and height h arranged in a circular patch of diameter D . The solidity of the patch/obstruction is defined by ϕ (the total planar area covered by cylinders), which is systematically varied ( 0.098≤ϕ≤1 ) by increasing the number of cylinders in a patch ( Nc ). A point source is placed at ground level upstream of the patch and its transport over and around the patch is examined. Time-averaged velocity and scalar fields, obtained from simultaneous planar particle image velocimetry-planar laser-induced fluorescence (PIV-PLIF) measurements, reveal that the characteristics of wake and flow above porous patches are heavily influenced by ϕ . In particular, we observe that the horizontal and vertical extent of the wake and scalar concentration downstream of the patches decreases and increases with ϕ , respectively. Here, the recirculation bubble is shifted closer to the trailing edge (TE) of the patches as ϕ increases, limiting the flow from convecting downstream, decreasing the scalar concentration and virtually ‘extending’ the patch in the streamwise direction. As the bubble forms in the TE, vertical bleeding increases and hence the concentration increases above the patch where the cylinders appear to ‘extend’ vertically towards the freestream.
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time-averaged-velocity-and-scalar-fields-of-the-flow-over-and-around-a-group-of-cylinders-a-model-experiment-for-canopy-flows
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Accepted/In Press date: 17 February 2022
Published date: 23 March 2022
Additional Information:
Funding Information:
The authors gratefully acknowledge the financial support from EPSRC (grant nos. EP/P021476/1 and EP/S013296/1).
Publisher Copyright:
©
Keywords:
Mixing and dispersion, Mixing enhancement, Turbulence control, Turbulent boundary layers, Urban fluid dynamics, Wakes
Identifiers
Local EPrints ID: 456382
URI: http://eprints.soton.ac.uk/id/eprint/456382
ISSN: 2633-4259
PURE UUID: da25bb98-f349-46c1-bff4-c3f9c05ec211
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Date deposited: 27 Apr 2022 15:30
Last modified: 17 Mar 2024 04:05
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Author:
Dea Daniella Wangsawijaya
Author:
Claudia Nicolai
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