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Turbulence and dispersion below and above the interface of the internal and the external boundary layers

Turbulence and dispersion below and above the interface of the internal and the external boundary layers
Turbulence and dispersion below and above the interface of the internal and the external boundary layers
This study has looked at the development of the internal boundary layer (IBL) over a block array close to a sharp change in surface roughness and its effect on dispersion from a ground level source for ratios of the downstream distance to the roughness length of less than 300. This was done by comparing a Large--Eddy Simulation (LES) with inflow boundary conditions against a LES with inlet--outlet periodic boundary conditions and data from a wind tunnel experiment. The comparison showed that using inflow boundary conditions resulted in significantly better predictions of normal Reynolds stresses, mean concentration and scalar variance than when using periodic boundary conditions. In addition to established methods, an alternative approach based on the vertical Reynolds stress was used to evaluate the depth of the IBL as it developed over the array which enabled the location of the interface to be more clearly defined. It was confirmed that the IBL growth rate close to the change in surface roughness could be described by a power law profile, similar to the widely used power law formula with an exponent 0.8 for a ratio of the downstream distance to the roughness length greater than 1000. An analysis of mean concentration and turbulent scalar fluxes suggested that the presence of the IBL constrained the vertical development of the plume from a ground level source and so led to trapping of material in the canopy layer.
IBL, inflow turbulence, dispersion, urban environments
0167-6105
189-201
Sessa, Vincenzo
93db2e6d-48cb-4825-ad38-fc77f1e069a2
Xie, Zheng-Tong
98ced75d-5617-4c2d-b20f-7038c54f4ff0
Herring, Steven
15f891b4-1a9e-4ac8-af74-ce4158274451
Sessa, Vincenzo
93db2e6d-48cb-4825-ad38-fc77f1e069a2
Xie, Zheng-Tong
98ced75d-5617-4c2d-b20f-7038c54f4ff0
Herring, Steven
15f891b4-1a9e-4ac8-af74-ce4158274451

Sessa, Vincenzo, Xie, Zheng-Tong and Herring, Steven (2018) Turbulence and dispersion below and above the interface of the internal and the external boundary layers. Journal of Wind Engineering and Industrial Aerodynamics, 182, 189-201. (doi:10.1016/j.jweia.2018.09.021).

Record type: Article

Abstract

This study has looked at the development of the internal boundary layer (IBL) over a block array close to a sharp change in surface roughness and its effect on dispersion from a ground level source for ratios of the downstream distance to the roughness length of less than 300. This was done by comparing a Large--Eddy Simulation (LES) with inflow boundary conditions against a LES with inlet--outlet periodic boundary conditions and data from a wind tunnel experiment. The comparison showed that using inflow boundary conditions resulted in significantly better predictions of normal Reynolds stresses, mean concentration and scalar variance than when using periodic boundary conditions. In addition to established methods, an alternative approach based on the vertical Reynolds stress was used to evaluate the depth of the IBL as it developed over the array which enabled the location of the interface to be more clearly defined. It was confirmed that the IBL growth rate close to the change in surface roughness could be described by a power law profile, similar to the widely used power law formula with an exponent 0.8 for a ratio of the downstream distance to the roughness length greater than 1000. An analysis of mean concentration and turbulent scalar fluxes suggested that the presence of the IBL constrained the vertical development of the plume from a ground level source and so led to trapping of material in the canopy layer.

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Accepted/In Press date: 22 September 2018
e-pub ahead of print date: 26 October 2018
Published date: November 2018
Keywords: IBL, inflow turbulence, dispersion, urban environments

Identifiers

Local EPrints ID: 422001
URI: http://eprints.soton.ac.uk/id/eprint/422001
ISSN: 0167-6105
PURE UUID: f8dfc8ec-097e-46f6-870f-ea0a067fe294
ORCID for Zheng-Tong Xie: ORCID iD orcid.org/0000-0002-8119-7532

Catalogue record

Date deposited: 12 Jul 2018 16:31
Last modified: 22 Nov 2021 06:30

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Contributors

Author: Vincenzo Sessa
Author: Zheng-Tong Xie ORCID iD
Author: Steven Herring

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