Particle Dispersion Behavior Research In The Urban Underlying Surface Micro Model

The unique physical properties of the urban underlying surface bring huge difficulties and challenges to the study on the dispersion of pollutant particles. In order to investigate the mechanism of the particle dispersion in the urban underlying surface micro model, the aim of the dissertation is to simulate numerically gas-solid two phase turbulent flow and particle dispersion behavior in the urban underlying micro model with gas phase simulated by Large-eddy Simulation and the motion of the particle traced by Lagrangian trajectory model, and the influence of the building height on the flow field and the particle dispersion of the street canyon is also discussed. Above all, the particle dispersion above the street canyons under the condition of temperature inversion is analyzed, and the distribution of particle concentration is also given. The simulation results show that the particles are imposed a thermophoretic force because of the temperature gradient, so the temperature inversion leads to the improvement of the particle concentration near-surface low-temperature. The research results provide theoretical basis for contaminant removal in the atmospheric environment and the formation mechanism of weather disasters. The results are concluded in detail as follows:(1) The simulation results of underlying surface two-dimensional street canyon model is consistent with the field survey data, and it not only verifies the reliability of LES but also illustrates the feasibility of our procedure. Furthermore, different sub-grid constants have different effects on the flow field structure. The research shows that the smaller the sub-grid constant is, the smaller the eddy scale.(2) From the three dimensional scale, we simulate the flow field of the street canyon structure with three height-to-width rates and analyze that how the height-to-width rate influence the flow field and the turbulence structure. What’s more, we also reveal the dispersion of different size particles in the street canyon.(3) Considering the temperature inversion in the three dimensional model, we explore the temperature gradient’s influence on the particle dispersion, and give the particle concentration field. The simulation results show that the temperature has different effects on different size particles. In addition,the simulated condition at present is different from the actual condition, mainly because of large turbulent fluctuation. So there are certain differences between the turbulent transport of particles and thetemperature transport and the reality. As a whole, under the condition of temperature inversion, the particle concentration will get a lift close to the street canyon.