Modelling Sheltering Effects of Windbreaks in Open Spaces

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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

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Outline

1. Problems in urban open spaces
2. Development of Modelling Approach
3. Typology study
4. Wind tunnel tests
5. Applications
6. Residential site
7. Hospital entrance

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1 Problems in urban open spaces

• Windy places
• Windy city
• Site planning
• Inclusive design considering wind environment
• outdoor environments key element in urban life
  older people
• the effect of wind on peoples stability and
  freedom of movement outdoors, particularly for
  elderly weak patients, young mothers with push
  chairs,.
• Current wind comfort criteria
• Inconsistent
• For healthy adults
• Objectives

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Windy places

• Windy winter

A statistical analysis carried out at Heriot-Watt
University showed that, when the ambient
temperature is below 5C, the frequency of
occurrence of wind speeds exceeding 4m/s 73
in Aberdeen, 50 in Edinburgh 47 in
Glasgow During day time 0600 - 2200
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Worsened by planning, buildings

• Waverley Step first step into the city for many

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Favourable site for photo-generalists
Photograph from The Herald newspaper archive
http//www.theherald.co.uk/05/03/1955
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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

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Development of the Modelling Approach

• Methodology
• Validation

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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

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Irwin sensors
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The wind tunnel in Heriot-Watt
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Single block
Differencing schemes Speed
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Single block Results - KE profile _at_ X/D2
k-? model
RNG k-? model
2-layer k-? model
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Single block
Streamline comparison turbulence models
Experiment
2L k-? model
Standard k-? model
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• Single block Mesh/surface alignment

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Reattachment length of wake flow
Single block
XF
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
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Single block Mean velocity profiles
Z/H
Data range
1
X/H
0
1
2
3
4
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Comparison - velocity ratios
CFD1/CFD2
Exp.
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A pair of buildings
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A pair of buildings Results HH ?0, 15, 30,
60, 90o
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A pair of buildings Results H3H ?0, 15, 30,
45, 60, 90o
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Group of Buildings
Wind
L3
L6
L1
L5
L2
L4

• The investigated points in the streets are 2m
  high above ground level
• The velocities measured are horizontal wind speeds

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Computed flow field
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Group of Buildings CFD vs Wind tunnel data
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Group of Buildings The range of discrepancies

• 30 discrepancy between CFD and wind tunnel data
  is acceptable for environmental wind studies
• The 30 discrepancy range is shown by dash lines

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Buildings Vegetation(bluff bodies and porous
media)

• 2D sheet representation
• 3D representation

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Single sheet
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Single sheet
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Simple layout
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3 Applications CASE studies

• Residential site
• Hospital entrance

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3.1 Residential site

• A microscale plan Willow Tree Place, Edinburgh

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Wind tunnel modelling
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The layout and measuring points for comparison
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Results of comparison
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3.2 An hospital entrance
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The model
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The model

• Flow domain of 700m500m60m
• Cells 928949 with finest resolution about
  0.2m0.3m0.2m 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
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Pressure at the automatic doors
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Figure 5 comparison of wind pressure at the door
panel four arrangements (windbreak in three
porosities) at the entrance.
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Solid vs porous
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The windbreak
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The EndThank you