抄録
The flow separating on the upwind edges of the buildings affects strongly on the contaminant gas diffusion around the buildings. This paper describes the effects of the flow over the rooftops on gaseous diffusion around the models in connection with the flow conditions of the oncoming flow using by wind tunnel techniques. From the experiments, the following conclusions are confirmed. (1) The critical Reynolds number is determined to be equivalent to 10500 for the uniform flow, and 2100 for the boundary layer flow by considering the results of the flow patterns and the concentration distributions around two model buildings. (2) The height of the separated flow over the rooftops becomes lower as the turbulence intensity of the oncoming flow increases. (3) The length of cavity wake which stretches behind the high-rise model decreases as the turbulence intensity of the oncoming flow increases. It is approximately 5.8 H for √<u^2> / U_0 = 9.5 %. (4) Also, the length of cavity wake decreases as the power-law exponent of the wind velocity profile increases. It is approximately 5 H for α = 0.33. (5) The high concentration is found at the unwind rooftop position of the low-rise model because the tracer gas immediately reattaches on the rooftop by the eddy caused by the flow separating on the upwind edge of the low-rise model. The concentration decreases as the power-law exponent of the wind velocity profile increases. (6) For the small turbulent flow, the stream flowing downward along the leeward face of the high-rise model is generated because of the large eddy caused behind the model.
