Dispersion of a point-source release of a passive scalar through an urban-like array for different wind directions


Branford, S., Coceal, O., Thomas, T. G. and Belcher, S. E. (2011) Dispersion of a point-source release of a passive scalar through an urban-like array for different wind directions. Boundary-Layer Meteorology, 139, (3), 367-394. (doi:10.1007/s10546-011-9589-1).

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Description/Abstract

The dispersion of a point-source release of a passive scalar in a regular array of cubical, urban-like, obstacles is investigated by means of direct numerical simulations. The simulations are conducted under conditions of neutral stability and fully rough turbulent flow, at a roughness Reynolds number of Re τ = 500. The Navier–Stokes and scalar equations are integrated assuming a constant rate release from a point source close to the ground within the array. We focus on short-range dispersion, when most of the material is still within the building canopy. Mean and fluctuating concentrations are computed for three different pressure gradient directions (0°, 30°, 45°). The results agree well with available experimental data measured in a water channel for a flow angle of 0°. Profiles of mean concentration and the three-dimensional structure of the dispersion pattern are compared for the different forcing angles. A number of processes affecting the plume structure are identified and discussed, including: (i) advection or channelling of scalar down ‘streets’, (ii) lateral dispersion by turbulent fluctuations and topological dispersion induced by dividing streamlines around buildings, (iii) skewing of the plume due to flow turning with height, (iv) detrainment by turbulent dispersion or mean recirculation, (v) entrainment and release of scalar in building wakes, giving rise to ‘secondary sources’, (vi) plume meandering due to unsteady turbulent fluctuations. Finally, results on relative concentration fluctuations are presented and compared with the literature for point source dispersion over flat terrain and urban arrays

Item Type: Article
ISSNs: 0006-8314 (print)
1573-1472 (electronic)
Subjects: Q Science > QC Physics
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences > Aerodynamics & Flight Mechanics
Faculty of Engineering and the Environment > Engineering Sciences
ePrint ID: 172479
Date Deposited: 28 Jan 2011 08:25
Last Modified: 27 Mar 2014 19:20
URI: http://eprints.soton.ac.uk/id/eprint/172479

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