Effects on bulk scalar coefficient of wind angle, Development of scalar boundary layer and flow field near roughness

The authors performed wind-tunnel experiments to investigate bulk scalar coefficients between an urban-like 3 dimensional roughnesses and atmosphere using salinity method. In this paper, three main effects were investigated. Firstly, the effects of randomness of layouts of each block were discussed. Bulk scalar coefficients were measured on arrays with cubic blocks, whose angle against the wind were randomly changed. Secondly the sizes of scalar source were considered under three conditions of plan area indices with square and staggered array. The results showed that bulk scalar coefficients were affected by the size as mentioned in previous studies, however, the relation between geometrical conditions and the coefficients were independent with the size. Lastly, the effects of vertical mixture of air caused by roughness elements were discussed based on the measurement of wind profile for each array. This investigation showed that certain plan layouts might strongly affect on vertical exchange of air.