Transcript Modelling Sheltering Effects of Windbreaks in Open Spaces Fan WANG1, Wei LI2 and Chenghu Hu3 1School of the Built Environment, Heriot-Watt University, Edinburgh EH14

Modelling Sheltering Effects of
Windbreaks in Open Spaces
Fan WANG1, Wei LI2 and Chenghu Hu3
1School of the Built Environment, Heriot-Watt University,
Edinburgh EH14 4AS, UK
2Department of Aerospace Engineering, University of Glasgow,
Glasgow, G12 8QQ, UK
3Department of Architecture, Tokyo Polytechnic University,
Kanagawa 243-0297 Japan
Outline
1.
2.
Problems in urban open spaces
Development of Modelling Approach
1.
2.
3.
Typology study
Wind tunnel tests
Applications
1.
2.
Residential site
Hospital entrance
1 Problems in urban open spaces
Windy places
1.
–
–
Inclusive design considering wind environment
2.
–
–
outdoor environments key element in urban life older people
the effect of wind on people’s stability and freedom of
movement outdoors, particularly for elderly; weak patients,
young mothers with push chairs,….
Current wind comfort criteria
3.
•
•
4.
Windy city
Site planning
Inconsistent
For healthy adults
Objectives
Windy places

Windy winter
A statistical analysis carried out at Heriot-Watt University showed that,
when the ambient temperature is below 5°C, the frequency of
occurrence of wind speeds exceeding 4m/s
0
73% in Aberdeen,
50% in Edinburgh
47% in Glasgow
During day time:
0600 - 2200
360
30
25
24
Edinburgh Wind Rose
336
48
20
15
312
72
10
5
288
0
96
>15m/s
10~14.99m/s
264
5~9.99m/s
0~4.99m/s
240
120
144
216
168
Worsened by planning, buildings
Waverley Step: first step into the city for
many
Favourable site for photo-generalists
Photograph from The Herald newspaper archive:
http://www.theherald.co.uk/05/03/1955
1.4 Objective

Develop a tool that
can be used easily in design stage and
 model bluff bodies and porous media with
good accuracy and affordable computing cost

2
Development of
the Modelling Approach
Methodology
 Validation

Methodology
•
Validation cases
•
•
•
Single block
Pair of blocks (measured by Stathopoulos and Storm,1986)
Multiple blocks (measured by Stathopoulos and
Storm,1986)
•
•
•
Single windbreak
Windbreak with block
Model development
•
•
•
Turbulence model: k- model standard; 2-layer:
RNG
Differencing scheme: Hybrid; SMART; QUICK;
HLPA (hybrid linear/parabolic approximation)
Mesh/surface alignment
Irwin sensors
The wind tunnel in Heriot-Watt
1.0
Single block
Lyn Exp.
Durao Exp.
QUICK
SMART
HLPA
HyBrid
U/Ur
0.5
0.0
Differencing schemes
Speed
-0.5
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
5.0
6.0
7.0
8.0
X/D
1.0
1.0
Lyn Exp.
Durao Exp.
QUICK
SMART
HLPA
HyBrid
0.5
U/Ur
U/Ur
0.5
Lyn Exp.
Durao Exp.
QUICK
SMART
HLPA
HyBrid
0.0
0.0
-0.5
-1.0
0.0
1.0
2.0
3.0
4.0
X/D
5.0
6.0
7.0
8.0
-0.5
-1.0 0.0
1.0
2.0
3.0
4.0
X/D
Single block
Results - KE profile @ X/D=2
Y/D
2
measured locations
1
1
2
3
2.00
1.50
1.50
1.50
1.00
1.00
0.50
0.50
0.00
0.00
0.1
<KE>/(Ur)^2
0.15
Y/D
2.00
0.05
HYBRID
SMART
HLPA
QUICK
2-layer k- model
2.00
0
Lyn Exp.
RNG k- model
Y/D
Y/D
k- model
X/D
1.00
0.50
0.00
0
0.05
0.1
<KE>/(Ur)^2
0.15
0
0.05
0.1
<KE>/(Ur)^2
0.15
Single block:
Streamline comparison
turbulence models
Experiment
2L k- model
Standard k- model
Single block: Mesh/surface alignment
Single block:
Reattachment length
of wake flow
0.8
0.6
KE2L+SMART
KE+SMART
U/U
0.4
0.2
0.0
XF
-0.2
-0.4
-0.6
-2.0
-1.0
0.0
1.0
2.0
3.0
X/H
Experiment: XR = 1.61H, XF = 0.9H
2L k- model: XR = 2.16H, XF = 0.76H
Standard k- model: XR =2.16H, XF = 0.65H
4.0
Single block: Mean velocity profiles
Z/H
Data range
1
0
1
2
3
X/H
4
Exp
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
Z/H
2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
0
0
-1.0
-0.5
0.0
U/Ur
0.5
1.0
1.5
-0.5
0.0
0.5
U/Ur
1.0
KE+SMART
Mean velocity profile at X/H=4.0
Mean velocity profile at X/H=2.5
2
Z/H
Z/H
Mean velocity profile at X/H=1.5
KE2L+SMART
1.5
0.0
0.5
1.0
U/Ur
1.5
Comparison - velocity ratios
CFD1/
CFD2
Exp.
A pair of buildings
A pair of buildings
Results – H:H =0, 15, 30, 60, 90o
1.60
1.40
1.00
0.80
0.60
0.40
0.20
Wind angle = 0
0.00
0
5
10
15
20
Distance (m )
1.60
1.40
1.20
Q / Vr
Q / Vr
1.20
1.00
Wind angle = 60
0.80
0.60
0.40
0.20
0.00
0
5
10
Distance (m )
15
20
A pair of buildings
Results – H:3H =0, 15, 30, 45, 60, 90o
1.80
1.60
1.40
Q / Vr
1.20
1.00
0.80
0.60
0.40
0.20
Wind angle = 0
0.00
0
5
10
15
20
Distance (m )
1.80
1.60
Q/Vr
1.40
1.20
1.00
Wind angle = 60
0.80
0.60
0.40
0.20
0.00
0
5
10
Distance (m )
15
20
Group of Buildings
Wind
L3
L6
L5
L1
0
50
2.5m
10m 10m
2.5m
200
L4 L2


The investigated points in the streets are 2m high above ground
level
The velocities measured are horizontal wind speeds
Computed flow field
Group of Buildings
CFD vs Wind tunnel data
1.00
1.00
1.00
0.80
0.80
0.80
0.60
Qh/Vr
1.20
0.60
0.60
0.40
0.40
0.40
0.20
0.20
0.20
0.00
0.00
0.0
50.0
100.0
150.0
0.00
0.0
200.0
Distance from entrance (m )
50.0
100.0
150.0
200.0
0.0
Velocity ratios at L5
1.00
1.00
1.00
0.80
0.80
0.80
Qh/Vr
1.20
Qh/Vr
1.20
0.60
0.40
0.40
0.20
0.20
0.20
0.00
0.0
50.0
100.0
150.0
Distance from entrance (m )
200.0
150.0
200.0
0.60
0.40
0.00
100.0
Velocity ratios at L6
1.20
0.60
50.0
Distance from entrance (m )
Distance from entrance (m )
Velocity ratios at L4
Qh/Vr
Velocity ratios at L3
Velocity ratios at L2
1.20
Qh/Vr
Qh/Vr
Velocity ratios at L1
1.20
0.00
0.0
50.0
100.0
150.0
200.0
Distance from entrance (m )
Computation
Experiment
0.0
50.0
100.0
150.0
Distance from entrance (m )
200.0
Group of Buildings
The range of discrepancies
1.20
Computed values (Qh/Vr)
1.00
L1
0.80
L2
L3
0.60
L4
L5
0.40
L6
0.20
0.00
0.00
0.20
0.40
0.60
0.80
1.00
1.20
Measured values (Qh/Vr)
30% discrepancy between CFD and wind tunnel data is acceptable for
environmental wind studies
The 30% discrepancy range is shown by dash lines
Buildings + Vegetation
(bluff bodies and porous media)

1 3
Kr  
 1
2  2 
2D sheet representation:
3D representation:
2
0
Kr 
C
d
Adx
WSB
0
Kr 
 k dx
r
WSB

1 3
 1

2  2

kr 
WSB
2
Single sheet
Single sheet
1
Ke-2L model
Ke model
Ke-RNG model
Experiment
Wang's result
Wilson's result
0.5
0.25
2.50
0
2.00
0
5
10
15
20
25
30
X/H
1.50
TKE
U/Uo
0.75
1.00
Ke-2L model
Ke model
Ke-RNG model
Experiment
Wang's result
Wilson's result
0.50
0.00
0.00
5.00
10.00
15.00
X/H
20.00
25.00
30.00
Simple layout
1.6
1.4
Experiment
1.2
KE-2L
KE
1
U/Uo
0.8
KE-RNG
0.6
0.4
0.2
0
-4
-2
0
2
X/H
4
6
3 Applications: CASE studies
Residential site
 Hospital entrance

3.1 Residential site

A microscale plan: Willow Tree Place,
Edinburgh
Wind tunnel modelling
The layout and measuring points
for comparison
1.0
0.7
W
A
0.6
B
0.5
0.4
Y
0.0
X
L
Results of comparison
Y=0.6W
Y=0.4W
1.6
CFD simulation
Experiment
CFD simulation
Experiment
0.75
U/Uo
1.2
U/Uo
1
0.8
0.4
0.5
0.25
0
0
0
10
20
30
X (cm)
40
50
60
0
10
20
Y=0.5W
40
50
Y=0.7W
1
1
CFD simulation
Experiment
CFD simulation
Experiment
0.75
U/Uo
0.75
U/Uo
30
X (cm)
0.5
0.5
0.25
0.25
0
0
0
0
10
20
X (cm)
30
40
50
10
20
30
X (cm)
40
50
3.2 An hospital entrance
The model
The model



Flow domain of 700m×500m×60m
Cells: 92×89×49; with finest resolution about
0.2m×0.3m×0.2m at the entrance
Wind Conditions




NOBAL: 5.7m/s at 10m height, at NT291704
Most frequent wind: 6m/s from Southwest
Extreme wind: effective wind speed: 31.9m/s
(BS3699)
The windbreak:
Physical description
Fully open
Medium
Dense
Solid
porosity
1.0
0.5
0.3
0.0
Resistance
coefficient
0
2.0
8.0
Pressure at the automatic doors
1
0.9
0.9
0.8
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0.3
reduction ratio
0.2
0.2
average Cp
0.1
Wind Pressure Coefficient
pressure reduction ratio
1
0.1
0
0
Fully open
Medium
Dense
Solid
Figure 5 comparison of wind pressure at the door panel four
arrangements (windbreak in three porosities) at the entrance.
Solid vs porous
The windbreak
The End
Thank you