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