Wind Tunnel Simulation of Airflow and Dispersion of Pollutants over a Complex Terrain

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To study airflow and transport dispersion over complex terrains, field and wind tunnel experiments have been conducted for Mt. Tsukuba. The field observations were done under nocturnal inversion condition. Vertical profiles of wind velocity and direction by pilot balloons at five points, vertical profiles of air temperature by radiosondes have been done.<BR>The field observations show that together with nocturnal inversion, a stagnant zone upstream of a ridge and high wind on the lee slope develop.<BR>The wind tunnel simulation has been done in the Thermally Straified Wind Tunnel of National Research Institute for Pollution and Resources. The scale of the topographic model was 1/7500 for horizontal and 1/5000 for vertical. The nocturnal inversion was produced by heating airflow to 40°C and chilling the floor of the test section at 10°C. The wind speed was set at 0.4 m/s from the Froude number similarity. The results show that the transport dispersion under noctural inversion shows drastic changehdue to the relative height of source to the dividing streamline (DS). The vertical diffusion bellow the DS is restricted by the height, ie., pollutant does not go over the peak.<BR>On the contrally, the lateral diffusion becomes relatively large.<BR>For pollutants released above DS, the diffusion does not show essential differnces from that of adiabatic condition.
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