Post on 19-Apr-2019
ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Dispersion in urban areas
• Stephen Belcher• Professor of Meteorology• Department of Meteorology,
University of Reading, U.K.
Croucher Advanced Study Institute 2011-2012Urban Climatology for Tropical & Sub-tropical Regions
Lecturer’s Photo
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Figure 1. Aerial view of DAPPLE site
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ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Figure 1. Aerial view of DAPPLE site
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
What area would be contaminated?
• How does the plume disperse in urban area?– Need ground level concentration
– Decay with distance from source Cmax
– Horizontal spread of plume f• What aspects of city control this area?
– Building geometry– Street network
• What aspects of met control this area?– Wind speed & direction– Stability effects - ignored here
U
R
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Paradigms for ABL dispersion• Turbulence in ABL?
– Eddying motion moves material vertically and laterally– Parametrised e.g. in Gaussian plume model
• Advection along streets?– Material carried along streets– Branches at intersections
• Other effects– Tall buildings
• Groups• Isolated tall buildings
– Atmospheric stability• Unstable predominant category in UK cities
ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
The 2007 DAPPLE experiments
Wood et al (2009) Bull. Am. Met. Soc.
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Release strategy
Receptors fixed
Sources change with wind direction
3 tracers per expt
Wood et al (2009) Bull. Am. Met. Soc.
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Schematic flows
Belcher (2005) Phil Trans Roy Soc
Dobre et al (2005) Atmos. Env.
Balogun et al (2010) B.L. Met.
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Empirical results from DAPPLE
Or dosage = time integrated concentration
ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
0.001
0.01
0.1
1
10
100
0.1 1 10 100
R/H
0.001
0.01
0.1
1
10
100
0.1 1 10 100
R/H
Decay from source: Dmax(R)
• Normalization
• R/H < 4
– Not ordered
• R/H > 4
– Ordered
– Upper bound
rooftop wind
upwind
downwind
cross wind
channelled
D* DUH H 2
M
Field all wind
Wind tunnel SW wind
4 = 1 street length
Dmax AM
UHR2Solid: A = 12
Dotted: A = 6
R/L1 2 4
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
DNS: Direct Numerical Simulation
Branford et al (2011) B.L.Met
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Specification All motions resolved No turbulence model 6.7 x 107 grid points Wall time ~3 weeks 248 processors Re = u*H/ = 7000 Aligned + staggered arrays
16H x 16H x 8H
Direct numerical simulation
Red lines: water channel (Hilderman & Chong 2007)
Flow field reported in Coceal et al (2006)
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Mean concentration
Time and space average
Within canopy Above canopy
ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Concentration fluctuations
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
What disperses the material?
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Far field
Network region
What disperses the material?
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Far field
Network region
Entrainment flux
What disperses the material?
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Network model for dispersionNetwork model for dispersion
Soulhac PhD Thesis Ecole Centrale Lyon
Belcher (2005) Phil. Trans. Roy. Soc.
Hamlyn et al (2005) Atmos. Env.
Belcher et al (in prep)
Soulhac PhD Thesis Ecole Centrale Lyon
Belcher (2005) Phil. Trans. Roy. Soc.
Hamlyn et al (2005) Atmos. Env.
Belcher et al (in prep)
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Above canopy
Within canopy
Lateral turbulent transport neglected in canopy
Network model for dispersion
Calculate time and space averaged concentration C
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Street network model
Fij2
Fij3
Fij4
Fij1
Fij5
U
Fij1
Fi-1,j3
Fi-1/2,j5
Compute fluxes into boxes, where conc assumed well mixed
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Mathematical formulation
• Assume each street box and intersection box well mixed
• Balance fluxes into intersections and streets
• Parameterize fluxes– Advective fluxes along streets
– Diffusive exchange flux
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Solution for regular geometry
• Regular geometry, then:
• Where
– is fraction of flux lost to entrainment
– is fraction of flux going to right
– is fraction of flux going to left p 1 - p
p 1 - p p 1 - p
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
i j
n
k
p 1 - p
p 1 - p p 1 - p
k = 0 (n,k)
‘Leaky combinatorics’
Galton’s quinqunx
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Solution for regular geometry
• Solution is ‘leaky’ binomial distribution
– is number of intersections
– is position across array
• Solution tends to Gaussian for large np
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Comparisons with DNS
Goulart, PhD Thesis, University of Reading
Belcher et al (in prep)
ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Street Intersection
U 1.18 1.12
V 1.18 1.13
E 0.3 0.5
2 4 6 8 10 12 14 160
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
x/H
Con
cent
ratio
n/C
0,0
Model parameters
Variation of centreline concentration
DNS data
NM without re-entrainment
Nm with re-entrainment
Centreline concentration
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Uabv 3.5
Vabv 3.5
Kxx, Kyy 0.5
Kzz 0.3
Model parameters for above canopy
With re-entrainment
DNS data
NM without re-entrainment
Nm with re-entrainment
Centreline concentration
ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
5 10 150
0.1
0.2
y/H
Con
cent
ratio
n/C
0,0
5 10 150
0.1
0.2
y/H
Con
cent
ratio
n/C
0,0
5 10 150
0.02
0.04
0.06
0.08
0.1
y/H
Con
cent
ratio
n/C
0,0
5 10 150
0.02
0.04
0.06
0.08
0.1
y/H
Con
cent
ratio
n/C
0,0
2H 3H
6H 8H
Lateral concentration profiles
DNS data
NM without re-entrainment
Nm with re-entrainment
In-canopy lateral profile
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
In-canopy lateral profile
2H 3H
6H 8H
With re-entrainment
DNS data
NM without re-entrainment
Nm with re-entrainment
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
2/21/11
Above canopy concentration on centreline
0 5 10 150
0.02
0.04
0.06
0.08
x/H
Con
cent
ratio
n/C
s
0 5 10 150
0.05
0.1
x/H
Con
cent
ratio
n/C
s
0 5 10 150
0.02
0.04
0.06
0.08
x/H
Con
cent
ratio
n/C
s
1 2 3 4 5 6 7 8 910111213141516
123456789
10111213141516
x/H
y/H
Good agreement further from the source
Con
cent
ratio
n/C
0,0
0
0
0
0
Con
cent
ratio
n/C
0,0
0
0
0
Con
cent
ratio
n/C
0,0
Above roof concentration
DNS data
NM without re-entrainment
Nm with re-entrainment
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
2/21/11
5 10 150
0.1
0.2
2H from the source
y/H
Con
cent
ratio
n/C
s
5 10 150
0.1
0.2
3H from the source
y/H
Con
cent
ratio
n/C
s
5 10 150
0.1
0.2
0.36H from the source
y/H
Con
cent
ratio
n/C
s
5 10 150
0.1
0.2
0.38H from the source
y/H
Con
cent
ratio
n/C
s
Above canopy concentrationGood agreement further from the source
0
0
0
0
Con
cent
ratio
n/C
0,0
0
0
0
Con
cent
ratio
n/C
0,0
Con
cent
ratio
n/C
0,0
Con
cent
ratio
n/C
0,0
2H 3H
6H 8H
Above roof concentration
DNS data
NM without re-entrainment
Nm with re-entrainment
ASI2_Lecture 5_8/12/2011
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Back briefly to DAPPLE data
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Lateral spread of plume: f
Diamonds: wind tunnel measurements
Squares: full-scale measurements
Stars: branching network model
Blue: plume core (f > 0.65)
Green: plume edge (0.65 > f > 0.1)
Orange: outside plume (0.1 > f).
D R, Dmax R f R, Plot contours of f
Dashed line: Briggs (1973) spread
f BR
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ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Summary and conclusions
• Extensive measurements during DAPPLE experiments– Western Europe geometry– Complements Salt Lake City & Oklahoma City
• DNS for simplified geometries– All scales of turbulence computed– Useful for process studies
• Street network model– Streets and intersections: well mixed boxes– Works well for H ~ W– 3 regimes
• Near field - complex• Street network scale - network model works well• Far field - Gaussian plume sufficient
– Any good for Hong Kong?!
ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011
Stephen BelcherDepartment of MeteorologyUniversity of ReadingU.K.Tel: 0118 378 6646 Email: S.E.Belcher@Reading.ac.ukWebsite: http://www.met.rdg.ac.uk/~bl_met/index/
End, Thank You