Large-Eddy-simulation analysis of airflows and strong wind hazards in urban areas

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.