Thermal stratification effects on turbulence and dispersion in internal and external boundary layers
Thermal stratification effects on turbulence and dispersion in internal and external boundary layers
A synthetic-turbulence and temperature-fluctuation-generation method is developed and embedded in large-eddy simulations to investigate the effects of weak stable stratification (i.e. Richardson number Ri≤ 1) on turbulence and dispersion following a simulated rural-to-urban transition. The modelling approach is validated by comparing predictions of mean velocity, turbulent stresses, and point-source dispersion against data from a wind-tunnel experiment that simulates a stable atmospheric boundary layer (Ri= 0.21) approaching a regular array of uniform rectangular blocks. The depth of the internal boundary layer (IBL) that develops from the leading edge of the block array is determined using the wall-normal turbulent stress method proposed by Sessa et al. (J Wind Eng Ind Aerodyn 182:189–291, 2018). This shows that the depth and growth rate of the IBL are sensitive to the thermal stability and the turbulence kinetic energy (TKE) prescribed at the inlet, such that the IBL depth reduces as the TKE of the inflow is reduced while maintaining the same Ri, or as the Ri is increased while maintaining the same inflow TKE. When a ground level line source is introduced it is found that increasing Ri evidently reduces the vertical scalar fluxes at the canopy height, while increasing the mean concentrations within the streets. Furthermore, as with IBL development it is found that for a given value of Ri the effect of stratification becomes more pronounced as the inflow level of TKE is reduced, affecting scalar fluxes within and above the canopy, and volume-averaged mean concentrations within the streets.
IBL, dispersion, inflow turbulence, stable stratification
61-83
Sessa, Vincenzo
93db2e6d-48cb-4825-ad38-fc77f1e069a2
Xie, Zheng-Tong
98ced75d-5617-4c2d-b20f-7038c54f4ff0
Herring, Steven
15f891b4-1a9e-4ac8-af74-ce4158274451
1 July 2020
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
(2020)
Thermal stratification effects on turbulence and dispersion in internal and external boundary layers.
Boundary-Layer Meteorology, 176 (1), .
(doi:10.1007/s10546-020-00524-x).
Abstract
A synthetic-turbulence and temperature-fluctuation-generation method is developed and embedded in large-eddy simulations to investigate the effects of weak stable stratification (i.e. Richardson number Ri≤ 1) on turbulence and dispersion following a simulated rural-to-urban transition. The modelling approach is validated by comparing predictions of mean velocity, turbulent stresses, and point-source dispersion against data from a wind-tunnel experiment that simulates a stable atmospheric boundary layer (Ri= 0.21) approaching a regular array of uniform rectangular blocks. The depth of the internal boundary layer (IBL) that develops from the leading edge of the block array is determined using the wall-normal turbulent stress method proposed by Sessa et al. (J Wind Eng Ind Aerodyn 182:189–291, 2018). This shows that the depth and growth rate of the IBL are sensitive to the thermal stability and the turbulence kinetic energy (TKE) prescribed at the inlet, such that the IBL depth reduces as the TKE of the inflow is reduced while maintaining the same Ri, or as the Ri is increased while maintaining the same inflow TKE. When a ground level line source is introduced it is found that increasing Ri evidently reduces the vertical scalar fluxes at the canopy height, while increasing the mean concentrations within the streets. Furthermore, as with IBL development it is found that for a given value of Ri the effect of stratification becomes more pronounced as the inflow level of TKE is reduced, affecting scalar fluxes within and above the canopy, and volume-averaged mean concentrations within the streets.
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blm2019
- Author's Original
More information
Submitted date: 12 August 2019
Accepted/In Press date: 13 April 2020
Published date: 1 July 2020
Additional Information:
Funding Information:
VS is grateful to the Defence Science and Technology Laboratory and the University of Southampton for the funding of his PhD studentship. We thank the EnFlo team at the University of Surrey for providing the wind-tunnel data through the appropriate publications. We are also grateful to Prof. Ian P. Castro, Dr. Glyn Thomas, and Mr. Timothy Foat for helpful comments. The relevant data are available from the University of Southampton Institutional Repository, under 10.5258/SOTON/D1187.
Publisher Copyright:
© 2020, The Author(s).
Keywords:
IBL, dispersion, inflow turbulence, stable stratification
Identifiers
Local EPrints ID: 436815
URI: http://eprints.soton.ac.uk/id/eprint/436815
ISSN: 0006-8314
PURE UUID: 2bbceef1-a83f-479a-b695-97279d4ae486
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Date deposited: 10 Jan 2020 17:31
Last modified: 17 Mar 2024 02:59
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Author:
Vincenzo Sessa
Author:
Steven Herring
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