Large Eddy Simulation for 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.
Urban geometry, even simple obstacle arrays, has spatial heterogeneity, which makes it difficult to obtain a precise representative picture of the flow characteristics.
The unsteadiness or intermittency of canopy flows can be significant for the transport and dispersion of tracers. Mean flow patterns in street canyons can be roughly classified into some regimes. However, few studies have focused on the temporal variation of flow patterns in street canyons.
Turbulent organized structures (TOS) within and above the canopy are an interesting aspect of turbulent canopy flow. TOS in neutrally stratified turbulent boundary layer over a flat plate have been vigorously studied for over five decades.
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.
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