The Research Of Wind Environment In Near Ground Layer For Mountainous City Planning

As the social and economic developing, the target of urban development has beenchanged gradually from chasing the maximizing economic efficiency to the high-qualityurban environment creating.Most cities has the goals of building "livable city".However, most of the current design specifications and research are suitable for theconstruction of Plain City, but not enough for the special topography of mountain city aswell as lacking of guidance.Taking the mountain town as the research object, including the follow three mainparts as the research contents: wind environment data acquisition in the near groundlayer, planning objectification on ventilated corridor and urban wind environmentevaluation. Providing the beneficial reference for mountain town in the planning anddesign as the research purposes. This article is launched an in-depth study. The mainresearch contents include as below:Based on the measured data, five characteristics of wind environment in mountaincity near ground layer are summarized: annual average wind speed is low, whichbetween1.3m/s~1.5m/s. The static rate is quite high and some areas even up to41%.Wind speed and wind direction are uneven distribution, even located very close. Therehas a different wind speed and wind direction distribution. The wind direction is closelyrelated with the surrounding terrain and the same with mountain extension direction.The local circulation is very significant, such as mountain and valley winds. Theproblems of wind roses in the planning application is analysed and the method of windenvironment data acquisition when the environment lacking of wind roses is solved foran actual case. All of above can make the planning basis more reasonable and credible.The digital technology required for this study is established. Base oncharacteristics of wind environment in mountain city near ground layer, in order to builda fast, reliable simulation system as the goal, the impact of simulation accuracy andspeed of numerical simulation are discussed. Through the comparative analysis ofdifferent types of turbulence model and wall function, the Chen-Kim turbulence modelis suitable for simulation on large-scale outdoor wind environment and the RNGturbulence model is suitable for the local thermal circulation simulation. And thendescribed the GIS characteristics, functions, types and development overview.Analysized the concept and acquisition method of the digital elevation model (DEM). Based on the model data format and a variety of commonly used software, anew set of outdoor complex terrain rapid digital modeling method is used for realizingthe transformation between the network terrain file and CFD (PHOENICS) solid model.The model is generated directly by DEM data. From this method, virtual model and theactual terrain have the highest fit. Because of the integrated method, the time of urbanwind environment simulation cycle is saved in a large extent. This method provides aconvenient way to the research for urban wind environment.A more reasonable idea for urban wind environment simulation is proposed. Thedifferent simulation schemes are carried out for different planning stages. We shouldconsider the impact of the dynamic action for wind environment in urban scale windenvironment. Wind velocity in near ground layer is divided by wind speed classificationwhich provides better guidance for block construction under different wind velocity. Inthis research, instead of the plane, the terrain curved surface file is put into computer forsimulation. The result display problem of complex terrain is solved perfectly. Theimpact of the thermal and dynamic action for wind environment must be considered intypical local circulations (river wind and slope wind) at mountain city. And somespecific conclusions are drawn for the designers. With the decreasing of the slope, thewind speed at the top increased. The trend of the river wind penetrating into inner cityenhanced and the near surface wind speed of riverside area increased. The constructionmode of Yuzhong Peninsula riverside area is better than Shapingba, where the riverwind can move into inner city more deeply. In clear night, slope-land thermalcirculation effects the building internal wind environment significantly. The near surfacelayer wind velocity even reach up to more than1.5m/s when the slope angle is small.The high-rise buildings play a significant role in promoting the near surface wind speed,which is more suitable for mountain city where full-year wind speed is small.This research expounded the necessity and feasibility of the ventilation corridorsconstruction in the modern city. And give summarise of status quo of mountain cityventilation corridor. This paper expounded the different focus of the ventilation corridorconstruction between the new town construction and built-up areas transformation. Thenew town ventilation corridor planning and design focuses on a radical construction.Urban ventilation corridors construction must combine with the "oxygen resource"construction, which can make the greatest ecological benefits and perform an actualmountain town planning projects. Built-up area ventilation corridor planning and designshould give more focuses on seeking urban ventilation corridor. The concept of frontal area index is given by analyzing the traditional methods for determining ventilationcorridor. Building and terrain are proposed as the impact factors of frontal area indexcalculation method in mountain city. Use the frontal area index as an important indicatorto judge the main ventilation corridor. The traditional planning process by subjectivejudgment to determine the wind corridor is changd into quantitative analysis, whichfacilitate "urban acupuncture" fast and accurate implementation. Finally the keyprinciples are summarized on the process of ventilation corridor construction, whichshould provide a reference for the planning and design.Urban wind environment evaluation system is constructed with a combination ofqualitative and quantitative analysis for each subkey, and then the effect of urban windenvironment can be judged. Urban wind environment evaluation system fills thevacancies of the environment field, which forms a complete urban environmentevaluation system with thermal, acoustic and light environment evaluation system.