J.M. Crowther 1 , D. Mumovic 2 , Z. Stevanovic 3
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Transcript of J.M. Crowther 1 , D. Mumovic 2 , Z. Stevanovic 3
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ANALYSIS OF NUMERICALLY MODELLED LOCAL CONCENTRATION
GRADIENTS IN STREET CANYONS: IMPLICATIONS FOR AIR QUALITY
MONITORING
J.M. Crowther 1, D. Mumovic 2, Z. Stevanovic 3
1 School of the Built and Natural Environment, Glasgow Caledonian University2 The Bartlett, Faculty of the Built Environment, University College, London3 Institute of Nuclear Sciences, University of Belgrade
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Objectives of this study
• To analyse numerically modelled, local concentration gradients in street canyons
• To make recommendations for the positioning of air quality monitoring stations
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Cases Studied
1. A single street canyon
2. A staggered cross-road
3. An idealised complex configuration of several street canyons
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Methodology
• PHOENICS with different turbulence models:– Standard k-epsilon– Renormalisation group k- model– Chen-Kim modification of k- model– Two-scale k-
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Validation
• Comparison with air quality data collected for Glasgow city Council, Scotland
• Wind tunnel data from the University of Hamburg, Germany
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Incompressible, Steady-state Navier Stokes equations
0)U( ii
P)}uuUU({)U(U jjiijjiijii
ij32
ijjitji k)UU(uu
k = turbulence kinetic energy per unit massUi = mean velocity, ui = turbulence velocity P = pressure, = density, μ = dynamic viscosityt = turbulent viscosity
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Pollutant Transport Equations
}cu)C({)C(U iiiii D
C)/(cu iCti
Turbulence Contribution to the Pollutant Flux
Conservation of Pollutants
D = Laminar Diffusivity, C = Turbulent Schmidt No.
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General Transport Equation
SU iiii )()(
Property with source S and diffusivity
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Standard k- Turbulence ModelEquation S
Turbulent Kinetic Energy
k t/k (G-)
Dissipation Rate t/ (/k)(C1G - C2
)
ikkiikt UUUG )(
/2kCt
k=1.0, =1.314, C1=1.44, C2=1.92, C= 0.09
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RNG k- Turbulence ModelEquation S
Turbulent Kinetic Energy
k t/k (G-)
Dissipation Rate t/ (/k)(C1G - C2
) -
ikkiikt UUUG )( /2kCt
k=0.7914, =0.7914, C1=1.42, C2=1.68, C= 0.0845
)1(/)/1( 30
3 C /Sk
ijijSSS 2 )(5.0 jiijij UUS o= 4.38, = 0.012
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Chen-Kim k- Turbulence ModelEquation S
Turbulent Kinetic Energy
k t/k (G-)
Dissipation Rate t/ (/k)(C1G - C2
) + C3G2/k
ikkiikt UUUG )(
/2kCt
k= 0.75, =1.15, C1 =1.15, C2 =1.9, C3 = 0.25, C= 0.09
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Two-scale k-ε Turbulence model
Equation S Turb. k.e. (production range)
kp t/kp (G-p)
Turb. k.e. (dissipation range)
kT t/kT (p-)
Transfer rate (production range)
p t/p )k
Ck
GCk
GGC(
p
pp3p
p
p2p
p1p
Dissipation rate (dissipation range)
t/ )k
Ck
Ck
C(T
3TT
p2TT
pp1T
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ikkiikt U)UU(G ; Tpkkk
/kC/kC 2P2
t
(kp,p,1pC,2pC,3pC,C) = (0.75, 1.15, 0.21, 1.24, 1.84, 0.009)(kT,,1TC,2TC,3TC) = (0.75, 1.15, 0.29, 1.28, 1.66)
Two-Scale k- Turbulence Model Parameters
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Case 1: Single Street Canyon
• Hope Street, Glasgow
• Three-dimensional: wind direction at normal incidence
• Ref. Mumovic & Crowther, 2002
• Four different turbulence models
• Longitudinal single vortex
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Standard k- modelSingle Street Canyon Pollutant Dispersion
Case 1
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RNG k- modelSingle Street Canyon Pollutant Dispersion
Case 1
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Chen-Kim k- modelSingle Street Canyon Pollutant Dispersion
Case 1
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Two-Scale k- modelSingle Street Canyon Pollutant Dispersion
Case 1
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Comparison of a wind-tunnel study (Pavageau &Schatzmann, 1999)
with the RNG turbulence model
Case 1
Single Street Canyon
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Case 2: Staggered Cross-Road
• University of Hamburg wind-tunnel test
• Ref Mumovic, Crowther & Stevanovic, 2003a
• Ref. Mumovic, Crowther & Stevanovic, 2003c
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w in d
Case 2 Staggered cross-road
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Case 2 Staggered cross-road, Section B-B
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Case 2 Staggered cross-road, Section A-A
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Case 3: Complex Configuration of Street canyons
• Wind-tunnel study University of Hamburg
• Ref. Crowther, Mumovic & Stevanovic, 2003a, b
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Experimental Geometry
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Model Grid for Wind-Tunnel Simulation
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Case 3 Complex configuration of street canyons:vertical plane at centre of 5th cavity
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Case 3: Concentration distribution in the mid-height horizontal cross-section of the 5th cavity
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Experimental Concentration Contours: Horizontal Cross-Section, Mid-Height, 5th Canyon
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Local Concentration Gradients
Local concentration gradientswind incident
small large/mediumperpendicular upper leeward side
vortex centrelower windward side
lower leeward side (large)bottom of the canyon(large)
oblique upper leeward sidevortex centrelower windward side
lower leeward side(medium)bottom of the canyon(medium)
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Factors for Location of Monitoring Equipment
Practicality of
Location
Practicality of
Location
Levelof
Turbulence
Levelof
Turbulence
LocalConcentration
Gradients
LocalConcentration
Gradients
SuitableLocation
SuitableLocation