| In the context of global climate change and low-carbon life,the development of spatial layout and architectural forms that conform to regional climate has become an important research topic in the field of urban and rural planning and architecture.Due to its special historical and cultural background and climate environment,Kaifeng city has bred some blocks with local characteristics.However,with the change of The Times and the development of urbanization,many new buildings have been built in Kaifeng.Compared with traditional buildings,the form,scale and space use of new buildings have changed greatly.The emergence of new buildings not only changes the original architectural space texture,but also affects the ventilation environment at different scales from the city to the block.Under the trend of increasingly serious heat island effect in summer in Kaifeng area,the ventilation environment outside the building becomes worse and the local microclimate of the city becomes hotter,which has obviously affected the function and comfort of space use,and also brought negative influence to the traditional cultural tourism activities that Kaifeng has focused on promoting in recent years.Therefore,it is very necessary to create a good ventilation environment in cities and blocks to promote the sustainable development of cities.This study takes kaifeng old urban area as the research object and establishes a 3D model to simulate and analyze its outdoor wind environment.Firstly,according to the evaluation criteria of the main factors affecting urban ventilation and the wind environment in blocks,combined with the regional environment of Kaifeng,the relative comfort evaluation method was determined with the average wind speed,maximum wind speed,minimum wind speed and wind speed range as the main indexes,and the Green Building Evaluation Standard GB/T 50378-2019 as the reference basis.Secondly,based on the weather statistics of kaifeng in recent 30 years,the main wind direction and wind speed in summer and winter were analyzed and the boundary parameters of wind environment simulation were determined.Finally,this study takes The Song Du Imperial Street and its surrounding blocks in Kaifeng city as the case study,and the surrounding blocks of Shuanglong Street in Kaifeng city as the comparative case,analyzes and discusses the differences of outdoor wind environment between the two,and puts forward optimization strategies according to the comparative analysis results.The results of this study will help to improve the outdoor walking environment in Kaifeng,promote the construction of a more scientific and humane walking city,and thus increase the walking behavior of the city,protect the rights of pedestrians,and promote green,ecological and sustainable urban development.The main conclusions of this study are as follows:(1)The dominant wind direction in Kaifeng city in summer and winter is south wind and north wind respectively.In this study,the length,width and height of the building coverage area of the surrounding blocks of Imperial Street of Song Capital are 1136m×361.4m×64.1m,and the length,width and height of the building coverage area of the surrounding blocks of Shuanglong Street are 1134m×365m×28.8m respectively.Based on the requirements of the Cooperation organization for European Scientific and Technological Research(COST),The length,width and height of the calculation area of the Imperial Street block of Song Capital was set as 2097.5m×1322.9m×384.6m;Set the length,width and height of the calculation area of Shuanglong Street block as 1566m×797m×172.8m.According to the statistics of Kaifeng Meteorological Bureau,it is determined that the dominant wind direction in summer is south wind,and the average wind speed is 3m/s.In winter,the dominant wind direction is northeasterly,and the average wind speed is 3.6m/s.(2)PHOENICS software and K-ε turbulence model were used to accurately simulate and analyze the wind environment in the old city.According to relevant literature,the computational domain grid was divided into coarse,medium and fine grids in this study,and the total number of coarse,medium and fine grids was set as 915,400,2,009,600 and 3,290,600,respectively.According to the requirements of COST,the gradient air at the entrance boundary is set by gradient wind in the form of logarithm function.The outlet boundary is set as the free outflow boundary;As the buildings around the research object are mainly middle and high-rise buildings,the roughness coefficient of the underlying surface is set as 0.27.(3)The monsoon environment in both winter and summer has a great impact on people’s life.In summer,the highest wind speed was 6.089m/s,the lowest wind speed was 0.024m/s,and the overall average wind speed was 2.710m/s.The highest wind speed of Song Du Imperial Street in Kaifeng city in winter is 7.291m/s,the lowest wind speed is 0.014m/s,and the overall average wind speed is2.933m/s.Although the overall average wind speed of the block did not exceed the comfort evaluation standard in summer and winter,gentle wind and fresh wind appeared between some buildings,and the wind speed ranged from 5m/s to 6.9m/s,so the buildings would bring uncomfortable wind environment to people.(4)The monsoon environment of Shuanglong Lane block in Kaifeng city is suitable for people’s life in winter and summer.In Summer,the highest wind speed of Shuanglong Lane block in Kaifeng city is6.525m/s,the lowest wind speed is 0.013m/s,and the overall average wind speed is 2.800m/s.In Shuanglong Lane block of Kaifeng city,the highest wind speed in winter is 7.097m/s,the lowest wind speed is 0.005m/s,and the overall average wind speed is 2.930m/s.The wind speed ranges between 1.5m/s and 3.5m/s between most buildings in Shuanglong Lane block in summer and winter,so the buildings will bring people a more comfortable wind environment.(5)The layout of buildings,the orientation of buildings and the distribution of green space all affect the wind environment.The outdoor wind environment of the imperial Street block of Song Dynasty is the best when the building spacing is expanded by 10%.Through comparative analysis,the physical model of the Imperial Street of Song Capital in the old city of Kaifeng was transformed from three aspects of building layout,building orientation and greening.First of all,other variables are controlled unchanged,and the horizontal distance and longitudinal distance of buildings in The Imperial Street block of Song Du are reduced by 10%,widened by 10%,widened by 20% and widened by 30% respectively on the original basis.It is concluded that the outdoor wind environment of the block is the best when the building distance of Song Du Imperial Street block is expanded by 10%.Secondly,changing the orientation of the building reduces the Angle between the building and the wind,improving the ventilation of the whole block.Finally,some green belts were added to the larger open space in the block,which reduced the high wind speed in the block and made the wind speed distribution within the block more even. |
