EXPERIMENTAL STUDY OF TURBULENCE AND VERTICAL TEMPERATURE PROFILE
IN THE URBAN BOUNDARY LAYER
Kono, H., Tamura, D. , Iwai, Y., Aoki, T., Watanabe, S., Nishioka, M.*, Ito, Y.**, Adachi, T. ***
University of Hyogo, * Osaka Prefecture University, **Kaijo Sonic Corporation, ***University of Yamanashi
Introduction• Recently, the dispersion of motor vehicle exhaust gas has been
predicted using the new generation models in urban areas (Valkonen et al.,1995, Werferi, 1995).
• The Monin-Obukhov similarity theory has often been used in the models.
• However, the similarity theory cannot be applied within the roughness sublayer. (Rotach, 1993).
• The reason why the similarity theory can not be applied in the roughness sublayer is not known.
• Since the mechanical turbulence generated by buildings is large in the lower part of the urban boundary layer, the turbulence in the roughness sublayer may deviate from the empirical formula at rural smooth sites.
• We studied the turbulence and vertical temperature profile in the lower part of the urban boundary layer by conducting the field observations in Himeji City, carrying out wind tunnel experiments and numerical simulations.
Urban area in Himeji city the site of a microwave-tower, tethered balloon and the
Doppler sodar
Doppler sodar
Meteorological station
72 m tower
N
5km0
tethered balloon
View from the tower looking north
NorthIn the north of the tower is a commercial area with buildings of 10 to 45 m in height.
南
South
In the south and east of the tower is a commercial and residential area with buildings of 7 to30 m in height.
View from the tower looking south
Instruments mounted on the 72 m tower
Sonic Anemometer 54 m
southnorth
T 70m
T 60 m
T 4 0 m
T 18 m
T 4 m
50 Hz, 60 min
46 hours
April to August, 1996
Vertical temperature profileOne year
Thermistor thermometer (Espec RT-30S)
KAIJO SAT-550
Surface temperature
Infrared thermometer MR-40
turbulence
Summer
July 19, 2007 4: 00~ 11: 00
Measurement of vertical temperature at heights below 300 m
Using tethered balloon
Autumn November 8, 2007
5: 00~ 17: 30
At the park in the center of the city
0
50
100
150
200
250
300
5 7 9 11 13 15 17 19 21 23 25 27
θ (℃)
Z(m
)5 20 6 55: ~ :
7 35 8 15: ~ :
8 20 9 00: ~ :
9 00 10 05: ~ :
10 55 12 00: ~ :
12 00 12 50: ~ :
13 25 14 10: ~ :
14 15 15 10: ~ :
15 55 16 55: ~ :
17 00 17 35: ~ :
6
78
9
17 12
13
14
0
50
100
150
200
250
300
5 7 9 11 13 15 17 19 21 23 25 27
θ (℃)
Z(m
)5 20 6 55: ~ :
7 35 8 15: ~ :
8 20 9 00: ~ :
9 00 10 05: ~ :
10 55 12 00: ~ :
12 00 12 50: ~ :
13 25 14 10: ~ :
14 15 15 10: ~ :
15 55 16 55: ~ :
17 00 17 35: ~ :
6
78
9
17 12
13
14
Vertical profile of potential temperature and surface temperature in autumn (8 November, 2007)
RS
Lifted inversion layer
Neutral layer
Vertical profile of potential temperature and surface temperature in summer ( 19 July, 2007)
0
50
100
150
200
250
21 23 25 27 29 31 33θ (℃)
Z(m
)
5:00 6:00~
6:00 7:00~
7:00 8:00~
8:00 9:00~
9:00 10:00~
10:00 11:00~
11:00 12:00~
5
76
8
9
10
11
0
50
100
150
200
250
21 23 25 27 29 31 33θ (℃)
Z(m
)
5:00 6:00~
6:00 7:00~
7:00 8:00~
8:00 9:00~
9:00 10:00~
10:00 11:00~
11:00 12:00~
5
76
8
9
10
11
RS
Lifted inversion layer
unstable
B8 z- d=80m u=2.5m/ s σ w=0.47m/ s σ w/ u=0.19
- 3
- 2
- 1
0
1
2
3
8 383 758 1133 1508 1883
B8 z- d=140m u=3.6m/ s σ w=0.33m/ s σ w/ u=0.09
- 3
- 2
- 1
0
1
2
3
B8 z- d=190m u=2.7m/ s σ w=0.27m/ s σ w/ u=0.10
- 3
- 2
- 1
0
1
2
3
B8 z- d=240m u=2.5m/ s σ w=0.26m/ s σ w/ u=0.10
- 3
- 2
- 1
0
1
2
3w’(m/s)
u・t(m)
B13 z- d=80m u=3.0m/ s σ w=0.71m/ s σ w/ u=0.24
- 3
- 2
- 1
0
1
2
3
9 369 729 1089 1449 1809
B13 z- d=140m u=4.5m/ s σ w=0.47m/ s σ w/ u=0.10
- 3
- 2
- 1
0
1
2
3
B13 z- d=190m u=4.3m/ s σ w=0.62m/ s σ w/ u=0.14
- 3
- 2
- 1
0
1
2
3
B13 z- d=240m u=5.3m/ s σ w=0.82m/ s σ w/ u=0.15
- 3
- 2
- 1
0
1
2
3
u・t(m)
w’(m/s)
(a) 5:00- (b) 11:00-11:00 - 11:10
w' on 19 July (2007) measured by using Doppler sodar in Himeji city
Inversion layer
5:00 -5:15 Convective
turbulence
Neutral layer, RS
1000 m
1000 m
Summary results of turbulence measured at the towerat z = 54 m
Observation period: Apr. 1, June 12 – 15, Aug. 21, 24, 2006, n = 46
50 Hz, 60 min,
Wind directions: southern( SW – ESE)
Observed u*/u at the tower (z = 54m) in Himeji citywind direction: SW - ESE
Businger et al. 1971(rural)
n= 46
Under unstable conditions, turbulence transports momentum less effectively in urban areas than in rural areas.
Panofsky et al. 1977 (rural)
Roth, 2000 (urban)
Observed σw/u* at the tower (z = 54m) in Himeji city
u* mechanical turbulence
σw both mechanical and convective turbulence
u*/σw large mechanical turbulence large
σw/u*
-1-0.8-0.6-0.4-0.200.20.40.60.81
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
(m/s) Neutralw’
u’ (m / s)
-1
0
1
2
-3 -2 -1 0 1 2
(m/s) Unstable
Vectors (u’, w’) observed at the tower
z=54 m
(Kono and Koyaby, 2005)Oct. 21, 9:00 – 9:20
in 1993
Aug. 2, 12 :00 – 12:20
Strong upward convection
R = - 0.4
R = 0
-0.8
-0.4
0.0
0.4
0.8
12 15 18 21 19 21 0 3 6 9 11
hr
u'w'w'T'
Aug. 2
R
Rw’T’
Ru’w’
Momentum flux, temperature flux, correlation between u’ and w’ and correlation between w’ and T’ measured at the tower (z=54m)
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
11 15 21 19 21 1 3 9 11hr
u'w'(m2/ s2)
w'T'(K m/ s)・
Aug. 2
u’w
’ w
’T’
( m2 / s2 )
( K・m / s )
(Kono and Koyabu, 2005)
- 0.3 < R(u’w’) < 0 unstable
Rural: - 0.35 < R(u’w’) < -0.2 (Kaimal and Finnigan, 1994)
R(w’T’) = 0.5 unstable (urban & rural)
Oct. 20 – 21, 1993
Urban: - 0.3 < R(u’w’) < 0
unstableRural: - 0.35 < R(u’w’) < -0.2 (Kaimal and Finnigan, 1994)
R(w’T’) = 0.5 unstable (urban & rural)
In urban areas, convective turbulence transports heat but transports momentum less effectively in unstable conditions.
Under unstable conditions, the eddy diffusivity at the lower part of urban boundary layer, is different from that calculated from the empirical formula at smooth sites using the Monin-Obukhov similarity theory.
Test section of the wind tunnel.
Re = 67,000
3m× 0.3 m× 0.3m
1.3 m s-1Wind speed
3m2.5m
Flow straightener
1.8 mm cube
x
z
18 mm cubes, in diamond arrays with 36 mm nearest-neighbour separation
U, -u’w’, σw, σu in the wind tunnel
00.20.40.60.8
11.21.41.61.8
2
- 7 - 6 - 5 - 4 - 3 - 2 - 1 0 1 2 3- u'w'/ u*
2
(z-d)
/δ
(x)
x=67cmx=167cmx=267cmRaupach data
0 1 2 0 1 2
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
U/ U∞
z-d
(cm
)
x=67cmx=167cmx=267cm
0 0.5 1 1.5 0 0.5 1 1.5
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 1 2 3 4 5 6
σ w/ u* (m/ s)
(z-d)
/δ
(x)
x=67cmx=167cmx=267cmRaupach data
0 1 0 1
Raupach, M. R. (1981) Conditional statistics of Reynolds stress in rough-wall and smooth-wall turbulent boundary layers
δ
00.20.40.60.8
11.21.41.61.8
2
0 2 4 6 8 10 12σ u/ u*
(z-d)
/δ
(x)
x=67cmx=167cmx=267cmRaupach data
0 2 0 2
Eddy size λ which has maximum energy in the wind tunnel λ = U / 2 n , d = h = 1.8 cm
RS
IS
Scaled with obstacle size
Scaled with height
LES was used to predict turbulent flow
in the roughness sublayer. • Adaptive research - CFD 2000
• Computational domain: (100 times as large as those in the wind tunnel) streamwise 150 m, span wise 22 m, normal direction 12 m grid spacing 0.33 m. 450×66×26 cells.
• Boundary conditions: The lower boundary: The 1.8 m cubes were placed in diamond
arrays. The lower boundary and the surface of cubes : the logarithmic
wind profile wall function for a smooth surface The upper and the both side boundary : free slip The inlet wind speed: 5 m s-1 (uniform)
Side view of calculated vorticity (ωx, ωy)
x
z
ωy
1.5
-1.5
1.5
-1.5
ωx
ω y
ω x
Streamwize vorticity
Spanwise vorticity
At y = 11 m (center)
x
z
View from the topωy, ωx
ωx
ωy
x
z
x
y
y
z
At z / h = 2.5
CONCLUSION In the upper RS, u* / u under unstable conditions, were close to
that under neutral conditions.
These values showed large deviations from the empirical formula presented by Businger et al.(1971) which fitted observations at rural smooth sites.
Therefore, under unstable conditions, turbulence transports momentum less effectively in urban areas than in rural areas.
I n the RS, the size of eddies having maximum kinetic energy
is scaled with the obstacle size, in the IS, it is proportional to the height. They were shown in the wind tunnel.
LES showed that eddies in the RS were directly generated by
cubes like wakes and they were transported downwind. The eddy structure in the RS is expected to be different from that
in the IS.
Thank you for your attention!
A visualization of the urban boundary layer and U, -u’w’/ u*2,
σw/u*, σu/u* in the wind tunnel. wind
36mm
wind
36mm36mm36mm
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
U/ U∞
z-d
(cm
)
x=67cmx=167cmx=267cm
0 0.5 1 1.5 0 0.5 1 1.5
00.20.40.60.8
11.21.41.61.8
2
0 2 4 6 8 10 12σ u/ u*
(z-d)
/δ
(x)
x=67cmx=167cmx=267cmRaupach data
0 2 0 2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 1 2 3 4 5 6
σ w/ u* (m/ s)
(z-d)
/δ
(x)
x=67cmx=167cmx=267cmRaupach data
0 1 0 10
0.20.40.60.8
11.21.41.61.8
2
- 7 - 6 - 5 - 4 - 3 - 2 - 1 0 1 2 3- u'w'/ u*
2
(z-d)
/δ
(x)
x=67cmx=167cmx=267cmRaupach data
0 1 2 0 1 2
Vertical profile of potential temperature and surface temperature in summer ( 19 July, 2007) and autumn
(8 November, 2007) in an Urban area of Himeji City
(a)Summer
0
50
100
150
200
250
21 23 25 27 29 31 33θ (℃)
Z(m)
5:00 6:00~
6:00 7:00~
7:00 8:00~
8:00 9:00~
9:00 10:00~
10:00 11:00~
11:00 12:00~
5
76
8
9
10
11
0
50
100
150
200
250
21 23 25 27 29 31 33θ (℃)
Z(m)
5:00 6:00~
6:00 7:00~
7:00 8:00~
8:00 9:00~
9:00 10:00~
10:00 11:00~
11:00 12:00~
5
76
8
9
10
11
0
50
100
150
200
250
300
5 7 9 11 13 15 17 19 21 23 25 27
θ (℃)
Z(m
)
5 20 6 55: ~ :
7 35 8 15: ~ :
8 20 9 00: ~ :
9 00 10 05: ~ :
10 55 12 00: ~ :
12 00 12 50: ~ :
13 25 14 10: ~ :
14 15 15 10: ~ :
15 55 16 55: ~ :
17 00 17 35: ~ :
6
78
9
17 12
13
14
0
50
100
150
200
250
300
5 7 9 11 13 15 17 19 21 23 25 27
θ (℃)
Z(m
)
5 20 6 55: ~ :
7 35 8 15: ~ :
8 20 9 00: ~ :
9 00 10 05: ~ :
10 55 12 00: ~ :
12 00 12 50: ~ :
13 25 14 10: ~ :
14 15 15 10: ~ :
15 55 16 55: ~ :
17 00 17 35: ~ :
6
78
9
17 12
13
14
(b) Autumn
RSRS
Lifted inversion layer
unstable
Instruments
• Sonic anemometer: KAIJO SAT – 550, 10Hz, 60 min• Temperature: at height 4 m, 18 m, 40 m, 60 m, 70 m• for one year• thermistor thermometer (Espec RT-30S)
• Surface temperature: infrared thermometer Eko Instruments Co. MR-40
• Doppler Sodar: KAIJO KPA200: sampling interval 3 s
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