Eleni Liapopoulou

The effect of urban geometry on microclimate

As the world is becoming more and more urbanised, the built environment of cities takes an increasingly important role, having various effects on building energy performance, thermal comfort, and even on human health and wellbeing. Urban microclimate studies are gaining popularity, and have been conducted in the past mostly using field measurements. However, in the last decades numerical approaches have emerged, due to the advancement in computational resources. Computational Fluid Dynamics (CFD) is a relatively easy tool to assess the urban microclimate, which can generate fairly accurate results.

The aim of this research is to understand the underlying complex relationships between urban characteristics and microclimate. It investigates not only typical urban characteristics commonly used to represent the urban density, such as site coverage, street width, and canyon ratio, but also the heterogeneity of urban morphology by calculating the deviation of urban variables. CFD simulations are performed to study the effect the aforementioned characteristics have on wind velocity and air temperature patterns.

The CFD simulations are performed using the standard k-ε turbulence model and Reynolds Averaged Navier Stokes equations. This is the model most commonly used in similar studies, since it is cost effective and less time demanding. The appropriate computational domain size and grid resolution for urban climate case studies are determined, as they can considerably affect the results. The areas under investigation have dimensions of 300x300m, located in the Greater London Area. Statistical analyses are performed to identify correlations between the urban variables and microclimate predictions. Urban morphology and its heterogeneity are found to have a significant impact, and they should be considered in urban climate studies. Finally, on the basis of analysis results, this research provides insights on improving microclimatic conditions in cities, and specifically on mitigating the urban heat island effect.