Flows across built environments are complex due to complex building geometry and high variability in atmospheric winds. Understanding flows across buildings is essential from building design to urban planning, with applications in building energy saving, urban ventilation, pollutant dispersion, comfort and livability, policy making, etc. Our lab specializes in urban wind field modeling, from building scale to urban scale. Using both experimental and numerical approaches, we aim to build the bridge linking fluid mechanics and urban environment modeling to better understand the physics of flows across buildings.

 

Building or canyon scale

Flows across an urban street canyon can be highly complex even with a simple building geometry. The wind field depends on the Reynolds number, which governs the scale of the flow. We hope to better understand the physics of flows across buildings and in urban street canyons by extracting the flow physics at different scale.

Figure 1: Flow field in an urban street canyon of aspect ratio 2.0 changes from the double-vortex regime to the single-vortex regime with increasing Reynolds number (Re).

 

Neighborhood scale

At the neighborhood scale, the interaction between buildings becomes important. Realistic, complex building geometry in a real built environment increases the difficulties to accurately model the flow at the neighborhood scale. We aim to seek the balance between accuracy and cost of modeling to improve outdoor ventilation and thermal comfort through building design, for example, incorporating building porosity to increase pedestrian-level wind speed to improve outdoor thermal comfort.

Figure 2: The wind fields at the pedestrian level with (left) and without (right) building porosity at the ground level.

 

City scale

There is a lack of studies at city scale in the tropics, hence we focus on tropical cities, especially in Singapore. We use mesoscale models such as the Weather Research and Forecasting model to study the urban heat island (UHI) effect and extreme weather events. The impacts of future development and climate change can be simulated in mesoscale models to provide guidance on urban planning and policy making.

Figure 3: The urban heat island intensity during pre-, heat wave, and post-heat wave in Singapore during the April 2016 heat wave event.