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The Role of Pedestrian Wind Comfort Studies in Building Design

Wind comfort studies are important in any building to ensure the comfort, safety and overall well being of urban inhabitants as well as passersby. Engineering simulation adds value by helping minimize undesirable effects that the project could generate.
By Arnaud Girin
February 3, 2020
Topics
Markets

The construction industry is constantly changing. Driven by technology advancements and ever-increasing sustainability standards, this progress is transforming the way civil engineers, urban planners and architects work.

With trends such as 3D printing, prefabrication and modular construction, green building and material innovation, the industry’s historical resistance to optimization seems to have reached a limit and software solutions are here to complete this modernization process. Besides the already embraced BIM technology, project management tools and engineering solutions are making their way into every construction project.

Software doesn’t only assist the building design process—increasing productivity and saving time and costs—but it can have a decisive effect on the performance or effects of new structures, preventing issues that could arise after the project is completed.

From the Flatiron Building in New York that opened in 1902 to the 20 Fenchurch Street skyscraper in London built as recently as 2014, the world has several examples of architectural projects that encountered problems after the buildings were finalized. While the first became famous for its unpredictable gusts of wind, 20 Fenchurch Street (nicknamed the “Walkie Talkie’ building) faced two problems. First, the facade was reflecting sunlight to the street below causing discomfort and even melting parts of cars—an issue later fixed with shading. Second, the tower creates a wind tunnel with extreme winds, putting pedestrians’ and cyclists’ safety at risk.

Besides wind tunnel testing, which is paramount in the later stages, engineering simulation can be used to identify design problems or optimization potential early in the design process. Studies that can be conducted include structural integrity with finite element analysis, as well as wind load analysis and pedestrian wind comfort simulation with computational fluid dynamics (CFD). The following case study includes an evaluation of the wind around the aforementioned Walkie Talkie building in central London.

Case Study: Pedestrian Wind Comfort Study for 20 Fenchurch Street Skyscraper

This analysis was performed from an internet browser using cloud computing to investigate multiple design scenarios, wind directions and profile conditions in parallel. Using 3D modeled data of the buildings around the Walkie Talkie building, the CFD analysis’ setup took only a few steps—flow domain definition, wind direction, profiles and real simulation time.

When the simulation runs were completed, the results were post-processed to visualize quantities such as velocity, vorticity and pressure at different locations. The transient effects captured by the solver can indicate time-dependent issues where vortices and gusting appear in narrow passages. The aim of this project was to assess the level of comfort and safety of pedestrians in the proximity of the Walkie Talkie skyscraper, as well as to identify potential design problems.

Pedestrian Level

CFD simulation analyzing pedestrian wind comfort around the Walkie Talkie building (Source: SimScale)

The image above shows the average velocity at the pedestrian head level (1.5m - 2m altitude) for one wind direction. Here, architects and urban planners can easily identify higher wind velocities around the corners of some of the buildings. This cornering effect can have an even stronger impact when two opposite buildings are subject to it and when the street is parallel to the wind direction—and it can be observed on the narrow streets on one of the sides of the building. Uncomfortable areas are the ones with 8m/s wind velocity and above, which are depicted in the orange and red zones.

Downdraft Effect

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There are more factors that come to amplify these high-velocity zones. One of them is due to the fact the Walkie Talkie is considerably higher than the other buildings in the area. Hence, the tall structure redirects the airstream down coming at its wind facing facade to the ground. This consequently creates a downdraft flow that will increase the velocity at the bottom of the structure, at the passerby level.

The Synergy of the Wind Effects

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The accelerated wind generated by the downdraught effect is directed toward the street area on the side of the building. The flow stream passing around the corner of the building gets further accelerated due to the cornering effect. The combination of the downdraught, cornering and channeling effects generates an area of high velocities at a low level, adversely affecting pedestrian wind comfort.

Conclusion

Wind comfort studies are important in any building or urban design project to ensure the comfort, safety and overall well being of urban inhabitants as well as passersby. As a standard part of such studies, engineering simulation adds value by giving engineers, architects, and urban developers a significant insight into their design and helping minimize undesirable effects that the project could generate.

by Arnaud Girin
With a mechanical design background, Arnaud Girin has worked for six years on design performance optimization with CFD and FEA tools. He is currently part of the SimScale team and is involved in simulation projects for multiple industries, with a focus on architecture, engineering, and construction.

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