Abstract
In order to know contaminant concentrations in the vicinity of buildings for control of environment in buildings and understand air pollution in urban area accurately, it is necessary to understand the gas diffusion in complex air flow near buildings. For this reason, I have made wind tunnel experiments on this problem in the last few years. I report the results of these experiments in two papers. In this first paper, mainly I report the results of experiments on cavity and it's reattachment point which exert a great influence on the distribution of contaminant concentration near buildings. Results. 1) Cavity region increases as H/Z_0 and W/H become greater (Fig.6). 2) In the leeward side of model, relationship between X_R and √<S> is linear. This relationship holds regardless of characteristics of incident flow and existence of reattachment point on model's upper surface (Fig.8). Relationship between X_R and log (H/Z_0) is linear when model is W/H=0.5, 1, ∞(two dimensional) and existence of reattachment point on model's upper surface is not observed. But when the existence is observed, X_R is constant in spite of change of H/Z_0 (Fig.7). X_R is approximately constant in spite of change of D/H when existence of reattachment point on model's upper surface is not observed. But when the existence is observed, X_R becomes greater as D/H becomes greater (Fig.13). 3) On model's upper surface, X_R does not change in spite of change of D/H (Fig. 11B). Relationship X_R and √<S> is linear and relationship X_R and log (H/Z_0) is linear too when model is W/H=1 (Fig. 14). 4) Between two plate models, X_R, with some exceptions, is equal to a single windward plate model's X_R (Fig. 10).
