The vertical wind velocity profiles dominate wind loadings acting on tall buildings. By AIJ (Architectural Institute of Japan) Recommendations for Loads on Buildings, velocity profiles are to be prescribed according to terrain conditions. The effects of terrain conditions can be treated by the surface roughness parameters such as the roughness length scale and the roughness density. These parameters, however, cannot fully explain the profile over urban areas since the urban buildings form a non-uniform roughness. In this study, numerical flow computations by LES (Large Eddy Simulation) are conducted to predict vertical wind velocity profiles over an existing urban area. The computed results are confirmed by the observation data obtained by a Doppler LIDAR (Light Detection And Ranging) system at neutral atmospheric conditions. Then the effects of roughness parameters to the velocity profiles are discussed by using present results. Finally evaluating equations are presented for predicting the power low index of vertical velocity profiles over urban buildings.
