Wind rose and urban airflow
The «Wind» tab draws the wind rose from the London weather file and a simulation of airflow between the buildings around the site.
Overview
The «Wind» tab shows the wind rose (observed statistics) and the airflow between buildings (simulation) on one screen. The airflow shows where wind passes around the site and where it is blocked. It is for concept-stage analysis.
How to use
- Choose the site and the radius
- On the «Wind» tab, choose the period (annual, spring, summer, autumn or winter)
- Read the observed frequencies on the «Wind rose»
- Choose the plan or 3D simulation and press «Compute the wind flow»
Wind rose
The wind rose collects the hourly wind direction and speed recorded at the station, in 16 directions. It contains no modelled values. The data are the EPW/TMYx weather files of climate.onebuilding.org (TMYx 2011–2025), the standard weather files of building simulation (the same files Ladybug and Grasshopper use).
Station
In London the UK edition uses the file for London Weather Centre, St James's Park (TMYx 037700), a station in central London. From Bloomsbury it is about 1.9 km away. The wind rose is the wind at the station, not at the site; the screen always shows the station name, the distance and the observation period. Wind speed is measured at the station's anemometer height, so speeds from different stations cannot be compared directly.
Simulation method
The airflow is computed for one direction: the prevailing direction of the chosen period. The method is the lattice Boltzmann method (LBM) with a Smagorinsky LES turbulence model, run on a GPU. Terrain from the Environment Agency LiDAR ground model is included. The result is the time average of the last part of the run.
Grid
The grid is fixed at 4 m: an 8 m street is 2 cells wide. Building heights are the LiDAR heights used everywhere in the UK edition (Environment Agency, 2016–2022). Where LiDAR gives less than 2 m (for example on buildings completed after the survey), the height falls back to the OpenStreetMap height, then OpenStreetMap storeys × 3 m, then 3 m.
Domain
The domain extends 400 m beyond the plate on every side; the margin is dropped from the result. CFD practice guidelines (COST Action 732, Architectural Institute of Japan) set the margin at 5 times the height of the tallest building or more; a fixed 400 m keeps the domain from changing with one extreme building.
Radius
The simulation accepts radii up to 1 km. Above that the computation grows with the cube of the radius. Plates can be drawn up to 1.5 km.
Views
- Wind rose: bar length is frequency, colour steps are speed, and the number at the centre is the share of calm
- Plan simulation: colour is speed and the texture shows the flow direction (line integral convolution). The view height can be changed
- 3D simulation: traced streamlines, coloured along their length, show acceleration in streets and slow air behind buildings
Reading the result
A speed at a single point is not guaranteed by this tool. The result is for reading the structure of the space: which street the prevailing wind enters and behind which block it stalls. It is useful for comparing massing options on the same site.
Limitations
This is not a validated wind assessment. Wind microclimate assessments for planning (for example under the City of London's wind microclimate guidelines) use wind tunnel tests or validated CFD over many directions; this simulation does not replace them.
- One direction only (the prevailing one); a full study weights all 16 directions by frequency
- No trees
- No wind tunnel validation against a real site
«Save PNG» keeps a note that the result is an early-design reference without wind-tunnel validation, for the prevailing direction only. «Save plate only» drops it; add the caption yourself.
Data sources
| Data | Use |
|---|---|
| EPW/TMYx weather file, London Weather Centre, St James's Park (climate.onebuilding.org, 2011–2025) | Wind rose and prevailing direction |
| Overture Maps (© OpenStreetMap contributors, ODbL) · Environment Agency LiDAR Composite 1 m (OGL v3) | Building footprints and heights |
| Environment Agency LiDAR DTM (Copernicus GLO-30 in gaps) | Terrain |