Visualization of city breathability based on CFD technique: case study for urban blocks in Niigata City

In this study, a CFD (computational fluid dynamics) technique is used to investigate the roles of urban geometry, wind direction, and wind velocity in an urban environment. By applying efficiency concepts originally developed for indoor environments, the term “ventilation” is used as a measure of city “breathability.” Two types of building geometries are considered—cases featuring simple building blocks and actual urban blocks—which represent the configuration irregularity of Niigata City. The results obtained in the simple building block cases indicate that the wind velocity is low, and the air temperature and scale of the ventilation efficiency (age of the air) are generally high in an area crowded with low-rise buildings. On the other hand, in the areas around high-rise buildings, the air temperature and age of the air are relatively low as a result of strong winds from higher altitudes. These tendencies can also be observed in the actual urban block case. These results demonstrate that the scale of the ventilation efficiency such as the age of the air is useful in quantifying a city’s breathability.Graphical Abstract

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