Numerical Simulation Of Urban Wind Environment Considering Atmospheric Stratification

In recent years,the urban building density increases rapidly,the forms of buildings become variable,and the urban spatial layout changes significantly,which contribute to great influence on urban wind environment.City as the most densely populated area,is affected strongly by urban wind environment in human comfort and structural safety.In order to study actual urban wind field changes precisely,more accurate and efficient simulation is necessary.At present,the study of urban wind field doesn't take account the effect of atmospheric stratification,and the modeling of urban building is inefficient.Based on the above issues,this paper provide an insight to research about urban wind field based on automatic modeling.In this paper,the simulation of urban wind environment considering atmospheric stratification is studied.Firstly,the fluctuating wind speed time series based on the harmonic synthesis method is realized by the self-made program.Secondly,LES(Large Eddy Simulation)numerical simulation of a single building under different atmospheric stable stratification conditions is conducted to study the effect of atmospheric stable stratification on the flow field characteristics and turbulent structure.Thirdly,LES numerical simulation is performed on multiple buildings under different atmospheric stable stratification conditions,and the combined effects of atmospheric stable stratification and building density on the flow field around the building are investigated.Finally,a new indirect modeling method is proposed and its rationality is verified,and CFD(Computational Fluid Dynamic)simulation of actual urban wind environment based on the indirect modeling method is carried out with some actual urban buildings as examples.The results show that the number of atmosphere stratification K has a significant effect on the flow field around a single building.The existence of atmosphere stratification will increase wind speeds in the downwind and crosswind directions,and the growth increases as K become larger;meanwhile,when K is less than or equal to 2,vertical wind speed and fluctuation will decrease,and vice versa.The wind field between ideal building groups is affected both by atmosphere stratification number and building density.While K is less than or equal to 2,the increase of building density may cause significant decrease of the wind speed in the downwind direction,however,the building density can makes little difference to the cross-wind wind speed;beyond that,the increase of building density will lead to the increase of vertical wind speed.The indirect modeling method proposed in this paper can be effectively applied to the simulation study of the wind environment of actual urban buildings.