Dispersion of a Passive Scalar Within and Above an Urban Street Network

The transport of a passive scalar from a continuous point-source release in an urban street network is studied using direct numerical simulation (DNS). Dispersion through the network is characterized by evaluating horizontal fluxes of scalar within and above the urban canopy and vertical exchange fl...

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Bibliographic Details
Published in:Boundary-layer meteorology 2018-03, Vol.166 (3), p.351-366
Main Authors: Goulart, E. V., Coceal, O., Belcher, S. E.
Format: Article
Language:English
Subjects:
Advection
Advection (Earth sciences)
Analysis
Atmospheric Protection/Air Quality Control/Air Pollution
Atmospheric Sciences
Canopies
Canopy
Computer simulation
Detrainment
Direct numerical simulation
Dispersion
Domain names
Earth and Environmental Science
Earth Sciences
Fluxes
Mathematical models
Meteorology
Numerical analysis
Numerical simulations
Parameterization
Research Article
Simulation
Turbulence
Turbulent fluxes
Urban areas
Velocity
Water pollution
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Summary:The transport of a passive scalar from a continuous point-source release in an urban street network is studied using direct numerical simulation (DNS). Dispersion through the network is characterized by evaluating horizontal fluxes of scalar within and above the urban canopy and vertical exchange fluxes through the canopy top. The relative magnitude and balance of these fluxes are used to distinguish three different regions relative to the source location: a near-field region, a transition region and a far-field region. The partitioning of each of these fluxes into mean and turbulent parts is computed. It is shown that within the canopy the horizontal turbulent flux in the street network is small, whereas above the canopy it comprises a significant fraction of the total flux. Vertical fluxes through the canopy top are predominantly turbulent. The mean and turbulent fluxes are respectively parametrized in terms of an advection velocity and a detrainment velocity and the parametrization incorporated into a simple box-network model. The model treats the coupled dispersion problem within and above the street network in a unified way and predictions of mean concentrations compare well with the DNS data. This demonstrates the usefulness of the box-network approach for process studies and interpretation of results from more detailed numerical simulations.
ISSN:0006-8314
1573-1472
DOI:10.1007/s10546-017-0315-5