LES study on unsteadiness and impact of urban wind based on coherent turbulence structures

As a result of recent redevelopment by construction of renewal buildings in Tokyo, many high-rise-building clusters tend to be distributed widely and sparsely in city. The roughness aspects of urban surface become heterogeneous. In order to examine wind impact on buildings and their surrounding spaces in view of wind resistance design or environmental evaluation, it is important to grasp the turbulent characteristics of approaching urban wind by clarifying coherent flow structures. This study applies LES based on BCM (Building Cube Method) to flow field for several 10km square area of Tokyo.  This numerical model is formulated on the very fine Cartesian mesh system utilizing the IBM. The relation between characteristics of velocity profile and information about roughness configuration of actual urban districts is provided on the basis of the LES results. Also, the observational data obtained by Doppler Lidar is used for the numerical validation. Then, focusing on the complicated geometry of urban surface, the unsteady characteristics of turbulence structures over actual urban canopy are analyzed and elucidated. Accordingly various kinds of coherent turbulent structures including unsteadiness and gust are provided based on their classification of generating mechanism.