Investigation On Different Turbulence Models On Predicting Wind-driven Pollutant Dispersion Around Industrial Buildings

With the development of green industry,the air quality around industrial parks where industrial production enterprises located has attracted increasing attention.The smoke and dust generated in the process of industrial production are dispersed or discharged after purification,and spread to the work area in the industrial park and the surrounding residential areas through wind load,which still affects the health of personnel to a certain extent.Therefore,in the period of design and layout of industrial parks,it is necessary to fully consider the pedestrian wind environment around the buildings,so as to reduce the accumulation of pollutants in the industrial parks through reasonable layout and optimization of ventilation between the buildings of industrial parks and surrounding living areas.Researchers usually use computational fluid dynamics(CFD)numerical simulation to analyze the wind environment of outdoor buildings and the law of pollutant dispersion,but the accuracy of the prediction results is often affected by the turbulence model chosen.The wind environment has instantaneous characteristics,so it is necessary to consider the prediction difficulty brought by gusts to the flow field.More and more studies show that the dynamic model has better prediction than the steady-state model,but the calculation time cost is relatively higher.At present,there are few researches on dynamic models that comprehensively consider the near-ground wind environment and pollutant diffusion around industrial buildings,and the design methods of transient models and the optimization of quick calculation ability are insufficient.In order to explore the dynamic characteristics of wind environment and pollutant dispersion in industrial parks and surrounding buildings,this paper intends to use instantaneous model for reasonable prediction of pollutant dispersion,further explore the differences and applicability of different dynamic models,verify the design of a rapid prediction model for pollutant dispersion in industrial parks,and effectively improve the computational efficiency through reasonable optimization of the grid.In view of the above problems,this study explores the reasonable prediction of pollutant diffusion based on dynamic models,and applies the research results to array buildings and semiopen building forms.Specific research contents are summarized as follows:(1)Three typical transient models are used to analyze the dynamic characteristics of the near-earth wind environment and pollutant dispersion,and a method for predicting pollutant concentration field is established.In this paper,the accuracy of simulation prediction of three transient models,namely large eddy simulation(LES),delayed separation Eddy simulation(DDES)and stress mixed Eddy simulation(SBES),was compared.The flow field and pollutant concentration field around a single building were simulated over time,and the time-average results of the flow field with periodic changes were analyzed.It is found that the SBES hybrid model can accurately reflect the instantaneous flow field characteristics around a single building,and has better time-saving potential.This simulation method can well simulate the separation and shedding of various vortexes caused by the flow around the building.Compared with the contours of the wind tunnel experiment,it also shows a good coincidence degree.(2)For SBES,the prediction accuracy of flow field characteristics of different k-ω models and subgrid-scale(SGS)hybrid models are compared.The simulation results show that the SST k-ω-WALE mode is more accurate than other modes.Further analyzing the influence of other calculation parameters,O-grid and embedded hybrid grid were tried in addition to the conventional standard hexahedral mesh.The variable analysis of the discretization time step(Δt)and dimensionless sampling time(t*)shows that when Δt gradually decreases to 0.0045 s and t* gradually increases to 288,the stable flow field is formed,and the pollutant concentration around the building fluctuates in a reasonable range.(3)According to the empirical parameter setting of single building verification experiment,the relevant boundary conditions and mixed model setting are applied to the common array buildings and semi-open buildings in the industrial park.The results show that the influence range of the high instantaneous concentration is 80% larger than that of the high average concentration.The influence range of instantaneous concentration in semi-open buildings is also extended by nearly 70% compared with the time average high value,and the predicted underestimated area of concentration is mainly concentrated on both sides of semi-open buildings.The risk of pedestrian exposure was assessed by the combined intake score(IF)of the introduced pollutants.Studies showed that the intake ratio of the relevant persons to pollutants was 0.001 acceptable range,and anything above 0.01 was considered unreasonable.