A METHODOLOGY FOR DIAGNOSIS OF MEAN AIR FLOW DISTRIBUTION WITHIN URBAN CANYON BASED ON LES OVER REALISTIC URBAN GEOMETRY

Abstract

 Large-eddy simulation based on lattice-Boltzmann method has been conducted, using different inflow conditions, over a realistic urban geometry including high-rise building area in Shinjuku. Three types of inflow conditions regarding the boundary-layer height and turbulence intensities were reproduced by extending fetch with roughness blocks. The effect of boundary-layer development on mean air flow fields under neutral atmospheric condition has been investigated in a target domain with identical building geometries. The ratio of mean wind speed at the same positions in the different cases corresponded well with the ratio of the friction velocities. This means that mean wind speed within the urban canyon normalized by a bulk friction velocity is solely determined by the building geometry. Therefore, we can reproduce a three dimensional mean wind distribution within the urban canyon diagnostically by referencing a regionally representative velocity scale, which is the friction velocity, and the preprocessed microscale simulation of the target urban district.