Similarity between velocity and scalar profiles over cubical block array

We have performed wind-tunnel experiments to measure velocity and scalar concentration profiles over urban-like roughness arrays and reveal important characteristics of scalar dispersion in the boundary layer over rough wall as follows. First, comparison of profiles reveals that the scalar concentration boundary layer depth reaches almost consistent depth of momentum boundary layer, meaning that scalar is passively transported or diffused in boundary layer. In addition, the development of the boundary layer is steeper than that of smooth surface. Secondly, aerodynamic parameters, such as roughness length and displacement height are determined for both momentum and scalar. It reveals that the roughness length of scalar is smaller than that of momentum by the order of 10^-2 and can be well estimated by well-known scale-similarity model. Thirdly, roughness function of the momentum and scalar are determined and compared with several previous results. The roughness function of scalar for the present study lies between that of smooth and rough wall because of scale effect of scalar and decrease of Re number dependency.