Research On Simulation Method And Application Of Urban Thermal Environment

Urban thermal environment affects human health,social economic development and natural climate change.In order to reasonably regulate the urban thermal environment,this paper establishes a set of rapid calculation methods to explore the impact of vegetation coverage rate on the urban thermal environment using a numerical simulation method.First,a rapid calculation method is proposed,which is suitable for numerical simulation of urban thermal environment,namely nested calculation.Through the numerical simulation of two ideal building groups,the results of nested calculations and traditional calculation methods are compared,and the factors affecting the accuracy of nested calculations are analyzed,i.e.,the size of the sub-calculation domain,the grid size of the large calculation domain,and the interpolation method.The results show that nested calculation can effectively reduce the computational complexity and has acceptable accuracy;the optimized sub-domain boundary position can get better results,that is,the distance between the inlet boundary and the building group is the same as the height of the highest building among the building group,and the distance between the top,side,and outflow boundaries and the building group are twice the height of the highest building among the building group;large computing domain grid size increases,the accuracy of nested calculations slightly drops;the inverse distance weighted interpolation has little difference with the result obtained by constant interpolation.Secondly,based on the nested calculation method and the idea of spatial averaging,two vegetation simplified models in urban mesoscale are established.One is the combination of porous media of single layer grid and standard wall functions,and the other one is the combination of wall source terms and standard wall function.By comparing with the numerical model of vegetation in urban micro-scale(benchmark model),errors in these two simplified models are analyzed.The results show that both simplified models can reflect the flow characteristics of the vegetation.By nested calculation,the flow field parameters in the vegetation area in two simplified models are consistent with that in the benchmark model,while the spatial distribution of the parameters above the vegetation area and on the left and right sides are different from that in the benchmark model.However,the numerical deviation is acceptable.Finally,a case study of Shaoshan City which has been converted from rural area to urban area is conduct using the simplified vegetation model.The thermal environment of Shaoshan city is simulated in three vegetation coverage rates to analyse the wind and temperature field in Shaoshan City.The relationship between vegetation coverage and the thermal environment in Shaoshan City is discussed based on the relative heat island intensity and the average surface temperature of the earth.The results show that the average surface temperature decreases 1.74°C for every 10% increase in vegetation coverage.With the increase in vegetation coverage,the turbulence intensity increases while the wind velocity decreases.The research results in this paper can provide a case for the rapid calculation of urban mesoscale numerical simulation,and guidance for urban vegetation planning and construction.