Winds in urban area are strongly diffrent from those nearby meteorological stations. Numerical tools bring accurate wind comfort assessment in new urban projects to wind engineering team and sustainable city development consultants.

1. Assessment of pedestrian wind comfort
in urban area with numerical tools

2.  Pedestrian wind comfort criteria
 Guidelines for wind comfort
 Influence of master plan on comfort mappings
 UrbaWind: a CFD tool dedicated to assessing the pedestrian
wind comfort
 Questions?
Contents

3. Pedestrian wind comfort
 Wind = air motion inducing forces on bodies => feeling, safety
 Winds in urban area are strongly different from those nearby
meteorological stations
How to design
the master plan?

4. Pedestrian wind comfort
 Wind chill, humidity, solar radiation, clothing are not considered
in the wind comfort criteria
 Wind comfort assessment of new urban project is common
practice in most wind engineering team
 Assessment methodology
Wind speed threshold + frequency of exceedance
Depends on the pedestrian activity
Depends on the country rules

5. Wind description
At each time steps the wind speed vector defined with 3 quantities:
- Main component: wind speed U
- 2 others orthogonal components: v and w
 Turbulent wind = tridimensional random process

6. 222
;; wvu wvu  
uUU  vVV  wWW 
U
I u
u

Turbulence intensity
 Random process => statistic description
1/ Computation of mean values
Mean speed and mean direction of the wind
2/ Split up in the mean value compared to the fluctuation
3/ Characterization of the fluctuations (turbulence): root mean
square
Wind description

7. Gust speed for safety (3 ’’-Eurocode) 85.2etmin10  T
Sampling duration T
0
TU
Gust speed definition  uTuTgust IUUU   1
gustU
Wind description
Wind speed for comfort (UK-Lawson)
Wind speed for comfort (France) 1etmin10  T
Wind speed for comfort (NL) 0eth1  T
0etmin10  T
MeanEquivalentGust
85.1/"3 GUSTcomfort UUWind speed for comfort (Canada)
Comfort threshold

8. Wind comfort categories
Wind comfort criteria are based on the frequency of wind speed
threshold exceedance and on the pedestrian activities.

9. Guidelines in the world
Wind comfort criteria are based on the frequency of wind speed
threshold exceedance and on the pedestrian activities.

10. First step: from the meteorological station to your project
How to assess the wind comfort?

11. Reference station:
Mast at 10m above the ground
Complexity of wind
patterns in urban area

12. Wind in any complex urban area
Venturi effect: speed up between two buildings or raws of buildings
Discomfort is mainly due to high winds

13. Wind in any complex urban area
Corner effect: speed up near the building corner
Discomfort is mainly due to transition and turbulence

14. Wind in any complex urban area
Wise effect: 3D vortices between 2 buildings
+ Vortices upwind any buildings
Discomfort is mainly due to high turbulent down-flowing winds

15. Wind in any complex urban area
Reality
 Mixture of all the effects: corner, vortices, venturi…
 Depends strongly on synoptic wind direction far above the
urban canopy
 Discomfort is based on frequency
of wind speed threshold exceedance
→Need comfort assessment studies
 Full scale experiments
 Scale down model experiments
 Numerical approaches (CFD)

16. Methodology to assess
the wind comfort
0
90
180
270
360
0 20 40 60 80 100 120
Wind direction (°)
0
1
2
3
4
5
6
7
8
0 20 40 60 80 100 120
Wind velocity (m/s)
Pedestrian comfort mappings
% of wind speed threshold
exceedance
Climatological data Urban wind simulation Climatological synthesis
Frequency table
Wind time series
Some wind directions

17. Methodology with UrbaWind
to assess the wind comfort
Comfort Mappings
STEP 2: DIRECTIONAL
COMPUTATION
DIRECTIONAL RESULTS
Gust and mean speed
STEP 1: SITE SET-UP
STEP 3: SYNTHESIS
Topography Buildings
Porous volumes
(trees, hedges)
Meteorological data
Mesh generation + Boundary conditions + CFD computations

18. Master plan : Buildings and
vegetation geometries
Meteorological data
Export data to design master plans
and buildings
Format: *.stl,
Recommended tool : Google Sketch Up, Autocad,
Rhinoceros
Met mast data: frequency tables or
timeseries (wind speed, direction,
standard deviation)
Format: *.stl,
Recommended tool: Google Sketch
Up, Autocad, Rhinoceros
Distribution and roses Mapping for comfort and wind energy assessment:
pictures and ASCII files
Data for Dynamic Thermal Software
- Distribution of air change rate: pictures
- Time series of air change rate: ASCII files
- Pressure coefficient on buildings: pictures and
ASCII files
Terrain modeling
UrbaWind
A CFD code dedicated to assess the wind
in any complex urban areas
Export wind characteristics at any
points in the urban master plan
Methodology with UrbaWind
to assess the wind comfort

19.  National Weather Data providers (sales services)
 Free Weather Data providers (Free)
 Weather data Tool (Software)
 Re-analysis weather data via Mesoscale numerical simulations (sales services)
Where may you collect
climatological data?

20. Providers Time series Frequency tables
Yes but need
conversion
Yes but need
conversion
EPW format: Yes No
EPW format: Yes No
Yes but need
conversion
No
Yes but need
conversion
No
Yes but need
conversion
No
Are they inputs for UrbaWind?

21. Ile Seguin (Paris-France)
Ingerop - Atelier Jean Nouvel
Examples

22. Examples
©
Block B3A of ZAC Paris Rive gauche
IVANHOE CAMBRIDGE - HINES France
Architect: Atelier Jean NOUVEL

23. Examples
©
Portes de l’Europe (Luxembourg)
Fonds Kirchberg

24. Computing performances
UrbaWind
Size (radius) and complexity Millions of Cells and
RAM
Time of computation
(1 wind direction)
100 m – 20 detached buildings 0.3 M – 0.4 Go 5 min
200 m – Suburbs 1.3 M – 1.6 Go 25 min
350 m – Suburbs 3.5 M – 4.2 Go 160 min
500 m – Downtown (height 100 m) 13 M – 16 Go 1200 min
Intel Xeon CPU E5-2609 2.4 GHz and 32 GB RAM (Urbawind 2.2 version)

25. Thank you!
www.meteodyn.com info@meteodyn.com