Impact of local terrain features on urban airflow
Impact of local terrain features on urban airflow
Past work has shown that coupling can exist between atmospheric air flows at street scale (O(0.1 km)) and city scale (O(10 km)). It is generally impractical at present to develop high-fidelity urban simulations capable of capturing such effects. This limitation imposes a need to develop better parameterisations for meso-scale models but an information gap exists in that past work has generally focused on simplified urban geometries and assumed the buildings to be on flat ground. This study aimed to begin to address this gap in a systematic way by using the large eddy simulation method with synthetic turbulence inflow boundary conditions to simulate atmospheric air flows over the University of Southampton campus. Both flat and realistic terrains were simulated, including significant local terrain features, such as two valleys with a width about 50 m and a depth about average building height, and a step change of urban roughness height. The numerical data were processed to obtain averaged vertical profiles of time-averaged velocities and second order turbulence statistics. The flat terrain simulation was validated against high resolution particle image velocimetry data, and the impact of uncertainty in defining the turbulence intensity in the synthetic inflow method was assessed. The ratio between realistic and flat terrains of time-mean streamwise velocity at the same ground level height over a terrain crest location can be >2, while over a valley trough it can be <0.5. Further data analysis conclusively showed that the realistic terrain can have a considerable effect on global quantities, such as the depth of the spanwise-averaged internal boundary layer and spatially-averaged turbulent kinetic energy. These highlight the potential impact that local terrain features (O(0.1 km)) may have on near-field dispersion and the urban micro-climate.
Above-ground-level height, Downslope, Street-scale terrain, Velocity modulation, Water tunnel experiment
189-213
Coburn, Matthew
0ee79550-a5f4-470c-a8eb-5354ee9369c8
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Herring, Steven
84ce6f2a-a728-4c9e-976a-178d94ae0a7e
Xie, Zheng-Tong
98ced75d-5617-4c2d-b20f-7038c54f4ff0
13 October 2023
Coburn, Matthew
0ee79550-a5f4-470c-a8eb-5354ee9369c8
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Herring, Steven
84ce6f2a-a728-4c9e-976a-178d94ae0a7e
Xie, Zheng-Tong
98ced75d-5617-4c2d-b20f-7038c54f4ff0
Coburn, Matthew, Vanderwel, Christina, Herring, Steven and Xie, Zheng-Tong
(2023)
Impact of local terrain features on urban airflow.
Boundary-Layer Meteorology, 189 (1-3), .
(doi:10.1007/s10546-023-00831-z).
Abstract
Past work has shown that coupling can exist between atmospheric air flows at street scale (O(0.1 km)) and city scale (O(10 km)). It is generally impractical at present to develop high-fidelity urban simulations capable of capturing such effects. This limitation imposes a need to develop better parameterisations for meso-scale models but an information gap exists in that past work has generally focused on simplified urban geometries and assumed the buildings to be on flat ground. This study aimed to begin to address this gap in a systematic way by using the large eddy simulation method with synthetic turbulence inflow boundary conditions to simulate atmospheric air flows over the University of Southampton campus. Both flat and realistic terrains were simulated, including significant local terrain features, such as two valleys with a width about 50 m and a depth about average building height, and a step change of urban roughness height. The numerical data were processed to obtain averaged vertical profiles of time-averaged velocities and second order turbulence statistics. The flat terrain simulation was validated against high resolution particle image velocimetry data, and the impact of uncertainty in defining the turbulence intensity in the synthetic inflow method was assessed. The ratio between realistic and flat terrains of time-mean streamwise velocity at the same ground level height over a terrain crest location can be >2, while over a valley trough it can be <0.5. Further data analysis conclusively showed that the realistic terrain can have a considerable effect on global quantities, such as the depth of the spanwise-averaged internal boundary layer and spatially-averaged turbulent kinetic energy. These highlight the potential impact that local terrain features (O(0.1 km)) may have on near-field dispersion and the urban micro-climate.
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Submitted date: 24 March 2023
Accepted/In Press date: 19 September 2023
e-pub ahead of print date: 13 October 2023
Published date: 13 October 2023
Additional Information:
Funding Information:
MC is grateful to the Faculty of Engineering and the Environments for providing the PhD studentship. MC and ZTX thank Drs Tim Foat and Davide Lasagna for providing insight and support. ZTX and MC are also grateful to the UK Natural Environment Research Council for providing financial support (NE/W002841/1) to the further data analysis and writing of the paper. The authors are grateful to the three anonymous reviewers for their valuable comments. Computational work was undertaken on the University of Southampton Iridis systems, and experimental work in the University of Southampton water tunnel.
Funding Information:
MC is grateful to the Faculty of Engineering and the Environments for providing the PhD studentship. MC and ZTX thank Drs Tim Foat and Davide Lasagna for providing insight and support. ZTX and MC are also grateful to the UK Natural Environment Research Council for providing financial support (NE/W002841/1) to the further data analysis and writing of the paper. The authors are grateful to the three anonymous reviewers for their valuable comments. Computational work was undertaken on the University of Southampton Iridis systems, and experimental work in the University of Southampton water tunnel.
Publisher Copyright:
© 2023, The Author(s).
Keywords:
Above-ground-level height, Downslope, Street-scale terrain, Velocity modulation, Water tunnel experiment
Identifiers
Local EPrints ID: 477240
URI: http://eprints.soton.ac.uk/id/eprint/477240
ISSN: 0006-8314
PURE UUID: e523c4a8-95c0-46db-8a7a-65e6512ef9ce
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Date deposited: 01 Jun 2023 16:52
Last modified: 13 Jun 2024 01:46
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Author:
Matthew Coburn
Author:
Steven Herring
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