Abstract
Air pollution and heat stress are major concerns associated with the liveability, resilience and sustainability of cities. They directly affect health and comfort and are associated with augmented morbidity and mortality and an increase in the energy demand for building ventilation, air cleaning and cooling. Nevertheless, the detrimental effects of poor air quality may partly be mitigated by increased urban ventilation. This strategy is closely related to the level of urbanization and the urban morphology. Therefore, detailed investigations on the impact of different morphologies on urban ventilation are of paramount importance. Computational Fluid Dynamics simulations have been widely used during the last decades to investigate the effects of the urban morphology on the urban ventilation. However, most of these studies focused on idealized building arrangements, while detailed investigations about the role of real urban morphologies are scarce. This study investigates the ventilation in a compact area in the city of Rome, Italy. 3D steady-state Reynolds-averaged Navier-Stokes simulations are performed to analyze the impact of Morphological Parameters (MP) on the urban ventilation. The results show a considerable worsening of urban ventilation with increasing building density with a reduction in the mean wind velocity up to 62% experienced at the pedestrian level (zp). Correlations between five MPs, e.g., plan area density, area-weighted mean building height, volume density, façade area density, and non-dimensional mean velocity at pedestrian level and at 10 m height are evaluated, and simple models are obtained using linear regression analysis. Among the selected MPs, the building façade area density shows a remarkable correlation with the non-dimensional mean velocity at zp (R2 = 0.82). Such correlations can be valuable tools for practitioners and urban designers, particularly during the first stage of planning, for highlighting areas potentially vulnerable to poor air conditions without running computationally expensive simulations.
Highlights
Nowadays, more than 55% of the world population lives in urban areas (United Nations, 2018a) and this number keeps growing due to the increase in number, size and density of cities (United Nations, 2018b), which are enlarging their environmental footprint
Since this study aims at assessing the impact of the urban morphology on the ventilation within a real compact urban area, the first step of the investigation is the identification of MPs, and their combinations, able to describe the different morphologies and quantify the building density and the vertical structures of cities
UP and U10 are the values at pedestrian level and at half of the average UC height (z10 = 10 m), respectively, while Uref is the mean velocity magnitude set at zP at the inlet plane
Summary
More than 55% of the world population lives in urban areas (United Nations, 2018a) and this number keeps growing due to the increase in number, size and density of cities (United Nations, 2018b), which are enlarging their environmental footprint. The challenge towards more sustainable and resilient built environments has become urgent, especially in existing cities. In this regard, the adoption in 2015 by all United Nations Member States of the 2030 Agenda for Sustainable Development is significant. In the Agenda, seventeen Sustainable Development Goals (SDGs) have been identified to guarantee prosperity. The third and the eleventh goals explicitly state that it is necessary to “ensure healthy lives and promote well-being for all at all ages” and to “make cities and human settlements inclusive, safe, resilient and sustainable” (United Nations, 2015)
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