基于风洞实验的丘陵下垫面气溶胶大气扩散特性研究

Study on Aerosol Atmospheric Dispersion Characteristic under Hilly Underlying Surface Condition Based on Wind Tunnel Experiment

核电厂正常运行或发生核事故时,会向大气释放一定量的放射性气溶胶,研究气溶胶在复杂下垫面的大气扩散特性对实现气载流出物辐射影响的准确评价具有重要意义。高斯烟羽或烟团模型被广泛用于大气扩散评价中,模型中的扩散参数描述了气溶胶受湍流作用扩散的强弱,需要针对不同的地形如平坦、丘陵下垫面进行校正。本文针对典型下垫面开展了气溶胶大气扩散风洞实验,采用激光粒子图像扩散参数估计方法,针对释放源高度不同的多组工况,统计分析了竖直截面内高分辨率的气溶胶浓度,根据高斯分布估计了下风向烟羽的上下边界及垂直方向扩散参数。结果表明:烟羽经过山体会出现整体抬升现象,这将导致山体后近地表浓度有所下降;烟羽经过山体前后出现浓度中心线两侧浓度分布不均现象,远离山体烟羽轨迹回归类高斯分布;释放源高度小于山体1/2高度的烟羽经过山体后轨迹趋于一致。高斯模型在丘陵下垫面适用度有限。

A certain amount of radioactive aerosols will be released into the atmosphere during normal operation of a nuclear power plant or in the presence of a nuclear accident.It is of great significance to study the atmospheric dispersion characteristics of aerosols under complex underlying surface conditions for the accurate evaluation of the radiative effects of airborne effluents.Gaussian plume or puff models are widely used in the evaluation of atmospheric dispersion.The dispersion parameters in these models describe the strength of aerosol dispersion due to turbulent flow.However,it needs to be corrected for different terrains such as flat and hilly underlying surfaces.The wind tunnel experiments of aerosol atmospheric dispersion under the conditions of flat and hilly underlying surface with Class D stability were carried out.The high-resolution aerosol concentration in a vertical section was statistically analyzed using a dispersion parameter estimation method based on laser particle image measurement.The upper and lower boundaries and dispersion parameters of downwind plume were estimated according to Gaussian distribution.The difference between the dispersion parameters of the flat underlying surface and the GB/T 3840—91 standard value is less than two times,which verifies the effectiveness of the method used.The plume trajectory of the hilly underlying surface condition indicates that the plume passes through the mountain and there is an overall elevation of the plume,which will lead to a decrease in the concentration near the surface after the mountain.In addition,there is an uneven distribution of concentrations on both sides of the concentration centerline before and after the plume passes through the mountain.The dispersion parameter in the part above the centerline reaches its maximum value at the windward slope.At the same time,the dispersion parameter in the part below the centerline reaches the minimum value at the top of the mountain.The plume trajectory returns to a Gaussian-like distribution after moving away from the mountain.The trajectories of the plume released from the source at 1/4,1/2 and 1 times the height of the mountain show that the plumes released at less than 1/2 the height of the mountain are blocked and lifted by the mountain,and the trajectories tend to be consistent.For the plume releases above 1/2 height of the mountain,the plume trajectory increases as the release height rises.The dispersion concentration distribution of plume in hilly underlying surface is beyond the applicability of Gaussian model.