analysis of numerically modelled local concentration gradients in street canyons: implications for...
TRANSCRIPT
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
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
Cases Studied
1. A single street canyon
2. A staggered cross-road
3. An idealised complex configuration of several street canyons
Methodology
• PHOENICS with different turbulence models:– Standard k-epsilon– Renormalisation group k- model– Chen-Kim modification of k- model– Two-scale k-
Validation
• Comparison with air quality data collected for Glasgow city Council, Scotland
• Wind tunnel data from the University of Hamburg, Germany
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
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.
General Transport Equation
SU iiii )()(
Property with source S and diffusivity
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
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
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
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
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
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
Standard k- modelSingle Street Canyon Pollutant Dispersion
Case 1
RNG k- modelSingle Street Canyon Pollutant Dispersion
Case 1
Chen-Kim k- modelSingle Street Canyon Pollutant Dispersion
Case 1
Two-Scale k- modelSingle Street Canyon Pollutant Dispersion
Case 1
Comparison of a wind-tunnel study (Pavageau &Schatzmann, 1999)
with the RNG turbulence model
Case 1
Single Street Canyon
Case 2: Staggered Cross-Road
• University of Hamburg wind-tunnel test
• Ref Mumovic, Crowther & Stevanovic, 2003a
• Ref. Mumovic, Crowther & Stevanovic, 2003c
w in d
Case 2 Staggered cross-road
Case 2 Staggered cross-road, Section B-B
Case 2 Staggered cross-road, Section A-A
Case 3: Complex Configuration of Street canyons
• Wind-tunnel study University of Hamburg
• Ref. Crowther, Mumovic & Stevanovic, 2003a, b
Experimental Geometry
Model Grid for Wind-Tunnel Simulation
Case 3 Complex configuration of street canyons:vertical plane at centre of 5th cavity
Case 3: Concentration distribution in the mid-height horizontal cross-section of the 5th cavity
Experimental Concentration Contours: Horizontal Cross-Section, Mid-Height, 5th Canyon
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)
Factors for Location of Monitoring Equipment
Practicality of
Location
Practicality of
Location
Levelof
Turbulence
Levelof
Turbulence
LocalConcentration
Gradients
LocalConcentration
Gradients
SuitableLocation
SuitableLocation