Abstract
Understanding the characteristics of urban airflows with complex geometrical features is very important from viewpoints of assessing strong wind hazards in the region. This study investigated turbulent airflows and strong wind hazards in an urban area by conducting large-eddy simulations (LESs) with explicit representations of buildings and structures. A business district, including historical architectures, of Kyoto City was chosen. The sensitivity experiments with realistic and idealized building arrangements indicated that the actual, complicated arrangement of buildings as well as the building height variability would enhance an unsteady nature of airflows in urban canopy. An analysis of strong wind hazards under a typhoon condition shows that sustained winds are stronger along streamwise-oriented major streets and over open spaces while instantaneous winds become stronger especially within areas with a mixture of high-rise buildings embedded in low-rise building areas/open spaces. It was indicated that wind gustiness increases with the decrease in building plane-area index. The analysis suggested that both the building height variability and the complex arrangement of buildings are considered to enhance the gustiness of surface winds. This study demonstrated that an LES model is practically useful for assessing the strong wind hazards in urban areas.
Highlights
Airflows in urban and/or populated areas determine the environmental conditions for our daily lives and activities
This study investigated the characteristics of turbulent airflows and their instantaneous peaks and thereby demonstrated potential hazards due to strong winds in an urban area as a case study for Kyoto City by employing an large-eddy simulations (LESs) modeling approach
The analysis of morphology of urban areas of Kyoto City in comparison to those of Osaka and Tokyo indicated that the geometrical features of an urban district in Kyoto City is characterized as having a high variability of building heights and a high density of building areas than those found in cities in Europe (Ratti et al, 2002), seen in the cases of Osaka and Tokyo
Summary
Airflows in urban and/or populated areas determine the environmental conditions for our daily lives and activities. Understanding how the variability of the height and distribution of buildings as seen in actual urban areas affects the urban airflows has been a challenging topic (e.g., Cheng and Castro, 2002; Kanda, 2006; Xie et al, 2008; Bou-Zeid et al, 2009; Nakayama et al, 2011; Zaki et al, 2011; Kanda et al, 2013; Park et al, 2015; Giometto et al, 2016; Nakayama et al, 2016; Castro, 2017; Han et al, 2017; Xu et al, 2017; Zhu et al, 2017; Li et al, 2018; Yoshida et al, 2018; Yoshida and Takemi, 2018; Hertwig et al, 2019) Under such urban geometrical influences, strong winds caused by tropical cyclones pose a great threat to urban areas.
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