Numerical Simulation Research On Atmospheric Pollutant Diffusion Under Different Temperature Stratification Conditions Based On OpenFOAM

Atmospheric pollution is one of the main environmental problems in the current society and is closely related to human health and economic development.Temperature stratification is an important factor affecting atmospheric pollution.In the real atmospheric environment,temperature stratification is constantly changing between neutral and nonneutral stratification.However,in atmospheric pollution studies,temperature stratification is often simplified to neutral stratification.In order to improve the accuracy of atmospheric pollution research,it is necessary to consider the impact of different temperature stratification on the diffusion of atmospheric pollutants.Based on OpenFOAM,this paper carried out a numerical simulation study of atmospheric pollutant diffusion under different temperature stratification conditions.The specific research content is as follows:(1)First,a detailed comparison of the relevant research on the diffusion of atmospheric pollutants under different temperature stratification conditions;according to the causes of temperature stratification,the realization of temperature stratification used in the study of different temperature stratification is analyzed.On this basis,the temperature boundary conditions used in the study of atmospheric pollutant diffusion under different temperature stratification conditions are determined.Secondly,the basic theory of the atmospheric boundary layer and computational fluid dynamics methods are introduced,and the method of adding dry and wet deposition and decay in the diffusion of atmospheric pollutants is explained.It provides a theoretical basis for the subsequent construction of a numerical wind tunnel.(2)Based on the OpenFOAM platform,a numerical wind tunnel that can be used to study the diffusion of atmospheric pollutants under different temperature stratification conditions is constructed.The main steps include:the development of the solver,the modification of the turbulence model,and the realization of the stratification boundary at different temperatures.The numerical wind tunnel is verified by classical experiments.For the velocity field,the average error between the simulated value and the experimental value is 14.2%;for the concentration field,the average error between the simulated value and the experimental value is 38.2%.The results show that the numerical wind tunnel can simulate the flow field characteristics better,and the concentration field needs to be optimized by adjusting the Prt number and Sct number.(3)A nuclear power plant is used as the research object,the numerical wind tunnel constructed in this paper was used to simulate the diffusion process of atmospheric pollutants under different temperature stratification conditions,and the velocity distribution,flow field structure and pollutant distribution around the nuclear island plant and the conventional island were analyzed.For the flow field,the temperature stratification tends to be more stable.The longer the separation flow reattachment length of the conventional island roof and the recirculation area length of the leeward side of the nuclear island plant are larger,but the impact height of the chimney outflow is lower;For the concentration field,the vertical diffusion height of pollutants is also reduced.(4)The flow direction,vertical and lateral concentration distributions of neutral and non-neutral(unstable and stable)stratification are deeply compared,and the diffusion law of atmospheric pollutants under different temperature stratification conditions is analyzed.The results show that with the increase of stability,the vertical and lateral diffusion ranges of pollutants gradually decrease;the maximum concentration value along the flow direction under the unstable stratification is the smallest,the neutral stratification is the largest,and the stable stratification is between the two.