High Rise and High Winds
Anyone who has ever walked near a very tall building in the middle of a city on a windy day will have noticed a strange effect. The wind is often much more intense around the base of the tower.
The growth in high rise buildings in major cities has been a growing concern. The City of London Corporation has promised a more “rigorous” assessment of developers’ predictions of ground winds.
Accelerated winds near skyscrapers are caused by the “downdraught effect”, says Nada Piradeepan, an expert on wind properties at Facade Engineering Consultancy firm Wintech. This happens where the air hits a building and, with nowhere else to go, is pushed up, down and around the sides. The air forced downwards increases wind speed at street level. There is also an acceleration of wind around the side of the buildings if it has completely square corners. If several towers stand near each other, there is also an effect known as “channelling”, a wind acceleration created by air having to be squeezed through a narrow space.
“These different effects can combine to create faster-moving wind. It’s complex,” says Piradeepan. “The downdraught effect is most strong where buildings stand face-on to the prevailing wind, which in London is from the south west.” More rounded buildings, such as London’s Gherkin, don’t have quite the same downdraught effect and don’t encourage an increase in wind speed around them, as the air doesn’t accelerate around corners, he adds.