Important aspects for succeeding with wind simulations
Mon 26 October 2020
The topic of wind comfort in cities has gained a lot of attention in Norway recently, following a news story from NRK about strong winds around high-rise buildings. This led to several responses; the consulting company Norconsult wrote about their experience in wind simulations and software developer Spacemaker also emphasized the high relevance of wind simulations. What everyone seems to agree upon is that simulating the wind environment is important, and that increased use of simulation can help create better urban environments. In this article we want to touch upon four important aspects for succeeding with wind simulations.
A wind simulation, as any fluid simulation, involves a lot of complex physics and mathematics. Modern simulation tools make it easy to get results, but getting reliable, trustworthy results is still a challenge. The problem starts already when defining the geometry, i.e. the terrain and the buildings in the urban environment. To get a good representation of the city environment, a large section around the main building must be included in the simulation. Creating the building geometry for a city district by scratch is too time consuming, hence, the geometry is typically imported from somewhere else. Additionally, simulation tools cannot resolve all details, so a simplified building representation is used. In a recent study, we showed that using building data from high-quality databases, such as Geodata’s 3D database for Norway, yield results in good agreement with 3D-scans. In comparison, data from popular open repositories such as OpenStreetMap were not of sufficient quality.
The next step is actually performing the simulation. Here, there are a multitude of choices to make, both in the computational modelling (e.g. choice of turbulence model, atmospheric boundary layer models) to how to solve the resulting governing equations (e.g. discretization schemes, pressure-velocity coupling). One way to obtain sufficient quality is to rely on consultants with sufficient experience in performing wind analysis. Another is to use bespoke simulation tools where the simulation settings are carefully tailored towards urban wind simulations. In ArchiWind we embed best practice guidelines into the software to make it easy for end users to create high-quality simulations without knowing all the intricate details.
Given these challenges, how can we work towards proper use of simulation tools in the industry? We propose the following four aspects:
Develop guidelines and regulations
The current regulations in Norway are at a generic level, usually only determining whether a wind analysis is required or not. Many cities around theworld have developed a more detailed set of regulations, also specifying what awind analysis should include and even how to create a proper simulation setup, such as the Wind Microclimate Guidelines for London.
Compare simulations against benchmark cases
A good way to ensure simulations sufficiently represent reality is to compare results against benchmark cases where high-quality simulation tools are available. Before asking someone to perform a wind analysis, you should ensure that they are aware of such benchmark cases and have validated their computational setup against them. One example of such a study is our comparison against experiments performed by the Architectural Institute of Japan.
Participate in the scientific arena
There is a large amount of research done within wind engineering. Wind engineering is an interesting research field, as a lot of the research has direct significance towards industrial aspects. One example is this article giving an overview of the use of simulation in urban physics and giving direct advice on proper simulation setup. Additionally, publishing in scientific journals ensures high quality results as you are continuously scrutinized by the top researchers and professors in the field through the peer-reviewing process.
Collaborate with real estate developers and architects
Understanding the needs and motivations of the developers in charge of the building project, and of the architects that design the building is important. It is essential that the output of a wind analysis has real value for the end user, which can only be obtained by communication and collaboration.