机动车排放NO_x扩散数值模拟及影响因素关联性

为研究大气风速、环境温度、尾气排热、地面热辐射及车辆拖动效应各因素对机动车排放污染物扩散的影响特性,建立实际大气条件下的机动车排放污染物NOx扩散的CFD仿真模型,进行三维非定常湍流流动的数值模拟,结合大气条件下的气象因素及NOx扩散浓度测试结果,得到各因素影响条件下的NOx扩散特性。结果表明,数值模拟结果与实测结果有较好的符合;在排放源高度以上范围,NOx的体积浓度随垂直高度增加呈现近似指数规律的衰减特征。大气风速增加,使NOx易于向风向下游扩散;环境温度、尾气温度、地面辐射温度增高及车辆运动速度提高使机动车排放污染物易于向上空扩散。应用灰色关联理论,分析了各影响因素之间的关联性,确定相应的关联序为大气风速>车辆运动速度>地表温度>大气环境温度>尾气温度。为研究大气污染物迁移扩散特性及污染物扩散理论模型系数的进一步修正提供理论依据。

Numerical Simulation on Diffusion of Automotive Emission NO_x and Grey Correlation of Influencing Factors

In order to study the diffusion characteristics of automotive emission NOx under conditions of the factors,such as wind velocity,ambient temperature,automotive exhaust thermal driving,ground thermal radiation and vehicle drag effect,affecting the dispersion of automotive emissions,the CFD simulation models of automobile emission NOx dispersion in real atmospheric environment were built.The numerical simulation of three-dimensional unsteady turbulent flow was achieved and the diffusion characteristics of automotive emission NOx with which affected by the every environmental factor were obtained.The results show that the numerical result accords relatively with the measured concentration by means of comparing with each other,and the dispersion characteristic of the pollutant can be well simulated with the models.The volume concentration of NOx shows approximately decreasing characteristics of exponential function with the increase of vertical height above the emission source.With the increase of the wind speed,NOx is easy to spread to the down-stream along the wind direction.Meanwhile,with the increase of atmospheric environment temperature,ground surface temperature,exhaust gas temperature and vehicle velocity,NOx is easy to spread to the sky.The correlation of factors affecting the automotive exhaust pollutant diffusion was analyzed with the grey correlation theory and the correlation sequence is atmospheric wind speed vehicle velocity ground surface temperature atmospheric environment temperature exhaust gas temperature,which can provide theoretical basis for the moving and dispersion of the automotive exhaust pollutants and modifying the coefficient of the theoretical models of atmospheric pollutants dispersion.