Wind Tunnel Experiment on the Footprint of a Block-Arrayed Urban Model in a Neutrally Stratified Boundary Layer

Abstract This study addresses the need to investigate footprint function features in urban areas and establish a validation database for numerical methods. Concentration and its flux footprints of a block-arrayed urban model were measured in a wind tunnel with a neutrally stratified boundary layer. The velocity and concentration were simultaneously measured by an X-probe hot wire anemometer and a fast-response flame ionization detector to evaluate the vertical flux. Experimental results highlighted the influence of the measurement heights on footprint distributions. Because the sensors were immersed in the roughness sublayer, their footprints showed strong heterogeneity across horizontal positions caused by building configurations. It was found that turbulent flux contributes up to 70% of total flux footprints, emphasizing the importance of accurate turbulent dispersion estimation in numerical methods. Furthermore, measured footprints were compared to those modeled by a widely used analytical method (Kormann and Meixner in Boundary-Layer Meteorol 99:207–224, 2001, https://doi.org/10.1023/ A:1018991015119). The measured footprints extended further along the streamwise direction and their spanwise dispersions were constrained by the rows of blocks, which failed to be reproduced in the analytical method. This indicates the significant effects of building configurations on footprint functions in urban areas.