FEB 2019, Luma Bendini

Can a single building change the wind microclimate of an entire area?

Let’s exercise ‘wind-intelligence’ by placing 3 famous buildings inside Central Park and analyze wind behavior around different building shapes. Because CFD is fun!

The effort to make wind-comfortable urban environments is one of the main challenges urban planners face nowadays. Cities are denser, and buildings are taller. Structures are inducing faster winds from higher altitudes to the ground level and affecting peoples’ perceived outdoor thermal comfort significantly.

The neighborhood area that will surround a new building today, might be significantly different in 5 or 10 years. Can wind studies evolve as fast as the cities, so that constructors are able to build long-term sustainable and comfortable urban spaces?

How the building shape affects wind perception in the area of interest

Back in the year 2000, while designing the Park Hyatt Towers, a 257 meters skyscraper in Chicago, a wind tunnel testing showed that the tower would be under significant effects of wake buffeting. It was provoked by northerly winds passing through the existing Johan Hancock Tower, a 343 meters high structure nearby.

As acceleration was way above desirable level, an extensive examination was performed after the first wind analysis. That resulted in changing the structure and shape to decrease acceleration: a 300-ton tuned mass damper was added to the projects.

The wind tunnel testing showed that Park Hyatt Towers would be under significant effects of wake buffeting provoked by northerly winds passing through the existing Johan Hancock Tower.

In increasingly dense cityscapes, taking in account the surrounding areas of an urban developments is a must! Especially when considering wind (and also light for that matter, but we are focusing on air flow here).

This is important to provide insights on major and minor aerodynamic modifications in order to either adapt a big structural system from the very early design stage, as the mentioned Chicago example, or to evaluate the need of canopy and other wind mitigation structures during later design stages.

So, is a single building capable of changing the wind microclimate of an entire area?

The inputs for this experiment are:

  • 1 of the world’s most famous neighborhoods: lower Central Park area, New York City.
  • 3 award-winning architectural projects: Flame Towers, Guangzhou Opera and The Gherkin.
  • Wind Simulations by Ingrid Cloud: one wind direction, same inflow velocity and visualization focused on pedestrian level (2 meters high).

Flame Towers, Azerbaijan
Opening: 2013
Height: 182 m

The streets in New York City are aligned in parallel, in this case even parallel to the inflow direction. Thus, without an object standing the way upstream, the wind would be split equivalently between these streets. However, the flow separation by the Flame Towers is causing the wind to accelerate in certain streets. If those streets are shopping areas or an important public transport location, it would require a closer examination to evaluate safety implications.

Guangzhou Opera, China
Opening: 2010
Height: 120 m

The freestanding concrete auditorium has a very irregular shape. Maximum height is 120 meters, while the overall structure is about 43 meters high, it’s a medium rise building. As it can be seen in the folloing two images, the wind is not significantly altered by adding this building. The wind dynamic around the highest nearby building is mostly affected by the imminent structure in its front.

St Mary Axe (The Gherkin), London
Opening: 2003
Height: 180 m

This is a very aerodynamic friendly shape, because the overall cylindrical geometry allows for the wind to move around the building, without being forced downwards. Curiously enough, the round shape creates a vortex (fluid flowing around a common axis) directing the wind to the rooftop of the neighboring building in the back. A rooftop open area would be struggling with this oscillating motion of the wind coming from the Gherkin.