Abstract
For the estimation of urban air quality, it is important to predict turbulent flows over buildings and structures, which are densely arranged in the urban area, and to clarify the dispersion process in the surface layer over very roughened surface. In this paper, it is the objective to determine the characteristics of flow and dispersion which change by arranging scatteringly the roughness blocks after making a spatially developed turbulent boundary layer over rough-wall by using LES technique and the pseudo-periodic boundary conditions. Two LES cases (uniform (staggered) arrays and random arrays )are carried out. Consequently, near the roughness height, touchdown in random arrays is earlier than that in uniform (staggered) arrays because of the local characteristic of roughness blocks. On the other hand, in the upper part, although there is no clear difference of streamwise fluctuating velocity between uniform arrays case and random arrays case, a great difference of mean and fluctuating concentration between both cases arise.
