Atmospheric boundary layer and scalar dispersion with explicitly resolved urban geometries using large eddy simulation for city (LES-CITY)

Understanding the relationship between turbulent flow characteristics and surface geometry is very important for mitigating urban atmospheric problems such as pollution and the heat island effect. The mean flow and turbulent statistics have been extensively studied by laboratory experiments, field campaigns, and numerical simulations. LES has a great advantage for investigating turbulent organized structures and the representative turbulent characteristics of canopy flow because it has high spatial and temporal resolution. Most of the previous applications of LES to urban surfaces were wind engineering studies of 3-D flows around a single obstacle. Few studies have applied LES to 3-D flow including obstacle arrays. In this study, flow structures and scalar dispersions in urban boundary layers are analyzed, using large eddy simulation (LES-CITY) with an explicitly resolved urban geometry. Two types of urban surface geometry have been investigated. One is large square/staggered arrays of uniform building with various areal densities (Experiment-1), and the other is a real 3-D building geometry using GIS-data of Tokyo Metropolitan area (Experiment-2).