Pedestrian Level Wind Velocity

The Power of Wind
Wind can be downright dangerous. Kitchener, Ontario built a new city hall a few years ago where the wind funnelled so hard against the front doors that people could not open them on windy days.

Three people on the outdoor jogging track on top of the first story of the Toronto City Hall were whisked into the air by a gust and dropped to the concrete below.

At most airports, the wind around the buildings can be so fierce that passengers making their way from planes to the terminal are blown off their feet.

What Causes Wind Problems?
Structures such as buildings, the surrounding terrain, landscape features, street corridors and open areas such as fields, parks, parking lots and bodies of water all significantly affect microclimatic wind patterns. Very often these features create or exacerbate wind problems at the pedestrian level. Some of the adverse effects buildings have on wind are shown below utilizing flow visualization in the water flume (flow is from right to left).


	Downwash Effect (Side View) The wind is deflected down to the street level, creating swirling turbulence at the pedestrian level.		Karman Vortex (Top View) Wind divides around a building, swirls on the downward side creating a vortex, resulting in that blast of wind as you turn a corner.
	Horseshoe Vortex (Side View) The downwash effect is intensified when wind curls up against an adjacent building.		Venturi Effect (Top View) Wind accelerates through narrow openings such as high buildings flanking narrow streets. Conditions are even more severe in tunnels.

Every object has an effect on the wind. To ensure the comfort and safety of people, architects, planners and engineers employ Theakston Environmental to consider building design, location of buildings, road placement, parks and open spaces.

Site Model:
Using Site and aerial photographs, survey footprint maps, and computerized digital data when available, Theakston technicians build an accurate physical scale model.

Testing:
The model is tested in a water flume where the movement of water simulates wind currents. Special wind velocity probes determine wind speeds at key locations and wind velocity under various wind speeds and direction scenarios.

Analysis:
A specially designed computer program processes the data collected. The analysis shows comfort levels of the key locations, pinpointing problems before construction.

Mitigation:
Areas identified as unsafe or uncomfortable through physical model analysis are mitigated with devices and subsequently tested at the facility to ensure the desired comfort criteria is achieved.