pedestrian wind comfort in urban area with numerical tools
TRANSCRIPT
Assessment of pedestrian wind comfort in urban area with numerical tools
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
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?
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
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
222 ;; wvu wvu
uUU vVV wWW
UI 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
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
Mean EquivalentGust
85.1/"3 GUSTcomfort UUWind speed for comfort (Canada)
Comfort threshold
Wind comfort categories
Wind comfort criteria are based on the frequency of wind speed threshold exceedance and on the pedestrian activities.
Guidelines in the world
Wind comfort criteria are based on the frequency of wind speed threshold exceedance and on the pedestrian activities.
First step: from the meteorological station to your project
How to assess the wind comfort?
Reference station: Mast at 10m above the ground
Complexity of wind patterns in urban area
Wind in any complex urban area
Venturi effect: speed up between two buildings or raws of buildings Discomfort is mainly due to high winds
Wind in any complex urban area
Corner effect: speed up near the building corner Discomfort is mainly due to transition and turbulence
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
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)
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
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
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
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?
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?
Ile Seguin (Paris-France)
Ingerop - Atelier Jean Nouvel
Examples
Examples
©
Block B3A of ZAC Paris Rive gauche
IVANHOE CAMBRIDGE - HINES France
Architect: Atelier Jean NOUVEL
Examples
©
Portes de l’Europe (Luxembourg)
Fonds Kirchberg
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)
