Abstract
Urban outdoor ventilation and pollutant dispersion have important implications for urban design and planning. In this paper, two urban morphology parameters, i.e. the floor area ratio (FAR) and the building site coverage (BSC), are considered to investigate their quantitative correlation with urban ventilation indices. An idealized model, including nine basic units with FAR equal to 5, is considered and the BSC is increased from 11% to 77%, generating 101 non-repetitive asymmetric configurations, with attention to the influence of plan density, volume ratio, and building layout on ventilation performance within urban plot areas. Computational Fluid Dynamics (CFD) simulations are used to assess the ventilation efficiency at pedestrian level (2m above the ground) within each model central area. Six indices, including the air flow rate (Q), the mean age of air (τP), the net escape velocity (NEV), the purging flow rate (PFR), the visitation frequency (VF), and the resident time (TP) are used to assess the local ventilation performance. Results clearly show that, fixing the FAR, the local ventilation performance is not linearly related to BSC, but it also depends on buildings arrangement. Specifically, as the BSC increases, the ventilation in the central area does not keep reducing. On the contrary, some forms with low BSC have poor ventilation and some particular configurations with high BSC have better ventilation, which indicates that not all high-density configurations experience poor ventilation. The local ventilation performance can be effectively improved by rationally arranging the buildings. Even though the application of these results to real cities requires further research, the present findings suggest a preliminary way to build up a correlation between urban morphology parameters and ventilation efficiency tailored to develop a feasible framework for urban designers.
Highlights
The urbanization process in the past few decades has accelerated the increase of urban density, which leads to significant differences between urban morphology and original form in natural conditions
This paper aims to investigate a quantitative correlation between urban-like geometries of different building site coverage (BSC) and six ventilation indices that are commonly employed in the literature
The floor area ratio (FAR) is kept constant at 5.0, while BSC gradually increases from 11% to 77%, resulting in a total of 101 asymmetrical idealized configurations
Summary
The urbanization process in the past few decades has accelerated the increase of urban density, which leads to significant differences between urban morphology and original form in natural conditions (such as number of streets, height of buildings, void spaces, etc.). Due to the compact urban spaces, air pollutant cannot be diluted and dispersed in time, causing a series of health problems [1]. With this rapid expansion of cities, especially for some developing countries, the relationship between the urban building density and the urban local wind environment has increasingly become the focus of attention. The density and morphological characteristics of buildings play an important role in the local ventilation performance and the dispersion of pollutants. Atmosphere 2019, 10, 33 is surrounded by buildings with a high density of pedestrians, the ventilation performance is very important for their comfort and health. Urban outdoor ventilation related to urban morphology can be assessed by full-scale field measurement, reduced-scale wind-tunnel or water channel experiment, and Computational Fluid
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