Numerical Simulation And Experimental Study On The Diffusion Of Airborne Pollutants In Wind Tunnels At Different Temperature Stratification

Atmospheric temperature stratification directly affects the turbulence activity,and then affects the diffusion ability of airborne pollutants in the atmosphere.It is very important for air pollution control and environmental control to explore the diffusion law of airborne pollutants under different temperature stratification conditions.At present,the research on the diffusion of airborne pollutants is mainly oriented to neutral stratified atmosphere,and the research on the diffusion of airborne pollutants under different temperature stratification conditions is not systematic and specific.Supported by the key project of National Natural Science Foundation of China,this paper takes a nuclear power plant as the research object,and studies the law of airborne pollutants diffusion under different temperature stratification by means of numerical simulation and wind tunnel experiment.The research contents include the following aspects:(1)The research contents of airborne pollutants diffusion at home and abroad are analyzed,and the main factors affecting airborne pollutants diffusion are summarized as follows: wind field,atmospheric temperature stratification,underlying surface,wet and dry deposition and pollution source characteristics.The determination of atmospheric temperature stratification is the main research factor in this paper.(2)The wind speed at different heights of a nuclear power plant was measured on site,and the wind speed profile was restored in the wind tunnel,and the deviation was less than 1.3%.The scaled model of the nuclear power plant was made at the scale of 1:1000,and the wind tunnel experiment of pollutant diffusion was carried out with SF6 as tracer.The experimental results show that the concentration of pollutants decreases with the increase of downwind distance,and the lateral diffusion range of pollutants gradually increases with the increase of downwind distance The variation of pollutant concentration with transverse distance presents normal distribution.(3)The effectiveness of CFD(Computational Fluid Dynamics)numerical model is analyzed by using wind tunnel test results,and the simulation results are evaluated by using model evaluation statistics method.The results show that CFD simulation results conform to the acceptable simulation performance range.(4)numerical simulation studies the stratification of different incoming flow temperatures(Ri=0.29,0.14,0,-1.5,-0.5,i.e.,strong stable,stable,neutral,unstable and strong unstable temperature stratification)and different local temperature stratification(temperature difference between atmosphere and surface,t = 56.9?,23.7?,8.1?,8.1?)The numerical simulation results show that:(1)There will be strong backflow in the area below 1/2 of the building height,and the velocity in the backflow area will decrease and the turbulence intensity will increase significantly.(2)The concentration of pollutants at each point in space increases with the increase of stability,and the diffusion distance of pollutants in downwind direction also increases with the increase of stability.(3)The temperature difference between the surface and the atmosphere affects the degree of pollutant downward diffusion.When the surface temperature is higher than the atmospheric temperature,the downward diffusion of pollutants is inhibited,and with the increase of temperature difference,the inhibition effect is more obvious.