Research On Urban Spatial Form In Cold Regions Based On Microclimate Improvement

The rapid development of cities has brought about many problems.The high density and high volume urban development model has led to the worsening of urban ventilation,air pollution,urban heat island and other climate problems.These problems not only reduce the comfort of the residents,but also seriously affect their health.The purpose of this study is to scientifically analyze the internal mechanism of the interrelationship between urban microclimate and urban morphology,so as to summarize the correlation between urban spatial morphology and urban microclimate and provide scientific guidance for urban planning.Based on the literature review,this paper summarizes the urban microclimate elements and urban morphology parameters by means of numerical experiments and regression analysis.Wind speed and temperature are used as microclimate evaluation indexes,and building density,volume ratio and layout are used as evaluation indexes of urban morphology parameters.Taking Harbin's high density urban area as the research object,the urban information model including underlying surface material and building height was established by using CAD and ArcGIS tools.Firstly,this paper elaborates the research status of architectural spatial form in different scales at home and abroad,and points out the fault phenomena that have been studied in urban mesoscale.Through literature review and investigation and statistics of the spatial form of Harbin,the factors affecting the microclimate of Harbin urban area are summarized.Finally,PHOENICS is used to simulate different urban spatial models,and the relationship between different influencing factors and urban microclimate is obtained.By combining two different scales of tools,Weather Research and Forecasting and Computational Fluid Dynamics(CFD),starting from the urban large-scale meteorological background,the study of urban microclimate in medium-scale and high-precision urban spatial microclimate is carried out.Firstly,using WRF mesoscale simulation technology,through adjusting boundary conditions,physical scheme parameters and meshing,the urban meteorological simulation with grid resolution of LKM and total research area of 50 km * 50 km was carried out.Then,the WRF output meteorological value is taken as the boundary condition of CFD simulation,and the micro-climate numerical experiment with a precision of 20 m is realized.Finally,compared with the field measured data,the results show that the average error of simulation in summer is 0.96 C,and that in winter is 1.55 C.The results of the overall numerical experiment have high reliability.The research shows that the change of building layout affects the spatialmicro-climate change,and the free layout is better than the enclosed layout in summer.In winter,the enclosed layout has higher temperature and better thermal stability than the free layout.Generally speaking,the multi-layer enclosure of medium intensity and medium density is the most suitable spatial form in the cold city of Harbin.In the study of influencing factors,building density has a positive correlation with temperature,and the temperature is stable between 20% and 25%,while the influence of volume ratio on temperature is more complex.Within a certain range(1-3.5),the temperature gradually increases with the increase of volume ratio.When the volume ratio is more than 3.5,the space temperature under the shadow shading effect is higher than 3.5.Degree has a downward trend.In terms of wind speed,with the negative correlation between building density and wind speed,when the density increases,the wind speed decreases;when the density is25%,the wind environment of pedestrian space is more suitable.Volume ratio is negatively correlated with wind speed.When the volume ratio is 1.5,the wind environment in pedestrian space is more suitable.Finally,this paper establishes a numerical experiment method of urban climate from macro to micro,and analyses the correlation mechanism between urban climate and urban morphological parameters.It can provide scientific,accurate and promising thermal environment optimization strategies for urban planning,urban design or built areas,which will help to improve cities.The scientific nature of planning and design provides theoretical support for the creation of sustainable and livable cities.