Wind rose and wind simulation

The «Wind» section draws the wind rose from the city's weather file and a simulation of the airflow between the buildings around the site.

Overview

The «Wind» section shows the wind rose (observed statistics) and the airflow between buildings (simulation) on one screen. The airflow shows where the wind passes through around the site and where it is sheltered. It is for analysis in the design stage. The wind simulation is part of the Pro pass (Pricing); the wind rose is also a plate in the free diagram set.

How to use

1. Choose the site and radius
2. In the «Wind» section, choose the period («Annual», «Spring», «Summer», «Autumn» or «Winter»)
3. Read the observed frequencies in the «Wind rose»
4. Choose «Simulation plan» or «Simulation 3D» and compute the wind flow

Wind rose

The wind rose sums up wind direction and speed from the EPW/TMYx weather file from climate.onebuilding.org in 16 directions. The file describes a typical meteorological year. It contains no measurement at the site.

Stations

The wind rose shows the wind at the station, not at the site. The screen always names the station, distance and period. Speed is measured at the anemometer height of the station; speeds from different stations therefore cannot be compared directly.

Simulation

The airflow is calculated for one direction: the prevailing wind direction of the chosen period. The method is the lattice Boltzmann method (LBM) with a Smagorinsky LES turbulence model on a GPU. Terrain from the DGM1 is included. The result is the time average of the last part of the run.

Grid

The grid is a fixed 4 m: an 8 m wide street is 2 cells wide. Building heights are the same as on all plates of the Germany edition (LoD2 3D building models, rules per city in Building heights and terrain).

Domain

The computational domain extends 400 m beyond the plate on each side; the margin is removed from the result. CFD guidelines (COST Action 732, Architectural Institute of Japan) set the margin at five times the height of the tallest building or more; a fixed 400 m keeps the domain from changing with a single very tall building.

Radius

The simulation accepts radii up to 1 km. Above that, the computing effort grows with the cube of the radius. Plates can be drawn up to 1.5 km.

Computing time

If several people compute at the same time, the jobs wait in a queue. The same site with the same settings comes from the cache.

Views

• Wind rose: bar length is frequency, the colour steps are speed, and the number in the centre is the share of calm
• Simulation plan: colour is speed and the texture shows the flow direction (line integral convolution). The height of the view can be changed
• Simulation 3D: streamlines coloured along their length show acceleration in streets and slow air behind buildings

Reading the result

This tool does not guarantee a speed at any single point. The result is for reading the structure of the space: which street the prevailing wind enters and behind which block it drops. It is suited to comparing massing options on the same site.

Limitations

• Only one direction (the prevailing direction); a full assessment weights all 16 directions by their frequency
• No trees
• No wind tunnel validation at a real location

«Save PNG» keeps a note that the result is a design orientation without wind tunnel validation and applies only to the prevailing wind direction. «Save plate only» leaves the note out; the caption is then added by hand.

Data sources

Related guides

• Thermal comfort
• Sun hours
• Data sources

Make diagrams