【作者】 刘吉营；

【导师】 余南阳； Jelena Srebric；

【作者基本信息】 西南交通大学 ， 供热、供燃气、通风及空调工程， 2013， 博士

【摘要】 过去二十多年来,国内外大多数研究采用RANS两方程湍流模型和LES模型来研究城市区域环境,由于城市区域环境的复杂性和较大的空间尺度,两种计算方法需要特别大的计算机资源,因此如何能够快速而又有效地预测非等温城市区域环境成为本研究的主要目标。本文首先分析目前城市风热环境的研究方法、城市环境CFD模拟技术、建筑外表面对流换热系数以及城区区域污染物对流传输的影响等研究进展,提出了本文的主要研究内容：(a)提供优化的零方程湍流模型(Zero-EQ),(b)研究不同街谷和建筑群分布的建筑外表面对流换热系数分布,(c)证明优化的零方程湍流模型以及壁面温度和对流换热系数组合的边界条件能够快速有效地预测城市热环境,(d)研究城市区域环境污染物对流传输的影响。详细的研究内容如下：本研究通过研读大量的参考文献和归纳总结长期的CFD计算经验,提出了城市区域环境CFD模拟设置常用的设定方法,包括湍流模型的选择,数值误差的确定,计算区域的设置,计算网格的划定,以及计算边界条件的设定等,建立了简化的CFD模拟设定分类,提供给研究者一些理论和经验的总结。本研究选用风洞实验对零方程湍流模型进行优化,分析实验数据,推导出优化的湍流涡粘度表达式,应用新的优化的湍流模型与风洞实验数据进行验证和分析。结果表明,在同等计算机配置下,Zero-EQ能够比MMK湍流模型快60%以上,是LES计算所需时间的1/10,同时Zero-EQ能较准确地预测多栋建筑周围流场的分布。考虑到重复不同工况风洞实验的局限性,本研究首先选择RANS两方程湍流模型来预测不同建筑群分布的流场分布,得到不同建筑群基于应变率和局部速度大小的涡粘度表达式(Zero-EQ2和Zero-EQ3)。利用上述风洞实验的研究结果(Zero-EQ1),选用不同的建筑群分布,对比三种模型的模拟结果与MMK湍流模型预测数据的优劣,得到Zero-EQ2和Zero-EQ3比Zero-EQ1更能够快速有效地预测建筑群周围流场分布的结论。本研究利用CFD模拟计算的方法对不同城市街谷高宽比(H/W)和不同平面面积密度(λp)建筑群分布(并行式和交错式)的室外表面对流换热系数进行研究,推导出不同建筑分布状况下的对流换热系数表达式,和选用风洞实验数据,和现场测试(宾夕法尼亚州立大学校园某学生公寓)数据,获取足够的计算边界条件和验证数据,减少计算区域网格,通过设置对流换热系数和温度边界作为壁面计算条件,来间接验证对流换热系数的准确性；应用零方程湍流模型计算城市街谷的热环境,得到与风洞实验吻合较好的数据,比RANS两方程湍流模型快一倍的速度,证明了其在工程应用领域的优势,同时指出零方程湍流模型对于浮力流动预测的局限性。另外,本研究中计算得到的对流换热系数表达式能够为今后继续能耗模拟研究提供足够的研究依据。本研究利用以上研究成果：优化的零方程湍流模型和建筑外表面的对流换热系数,研究二维城市街谷和三维建筑群的热环境对污染物浓度的影响。首先利用RNG湍流模型研究二维城市街谷的不同壁面受热条件下自然对流环境、混合对流环境和强迫对流环境下的速度分布、温度分布和污染物分布。由于零方程湍流模型不能较好地预测浮力流动,三维建筑群只选择强迫对流为主的热环境,选择入口与壁面温度差分别为ΔT=0℃和AT=10℃的两种边界条件,通过分析建筑群周围污染物的分布,验证了其快速预测污染物分布的准确性。最后本文选择成都市蒲江县寿安镇的某一生态建设项目,根据当地气象条件,通过研究寿安旧城区目前城市规划情况下的夏季城市热环境,分析不同区域的热环境特点,提供给新城区规划设计一些建议。EnergyPlus能耗计算最后应用于某一学生公寓建筑,来研究考虑周边建筑环境对流换热系数表达式的实用性。更多还原

【Abstract】 In the recent two decades, RANS and LES have been widely used to predict thermal environment in urban area. Due to the complex of urban area, two above common methods require large amount of computer resources to resolve the detailed flow field around buildings. Therefore, the main goal of this thesis is to enable quick and accurate simulations of wind flow over different urban terrains while accounting for a non-isothermal boundary layer. This research first analyzed current research status about the research method for studying urban environment, CFD simulation in urban area and the convective heat transfere coefficient at the external surfaces of buildings, and then provided the research content of this paper:(a) improve the Zero-equation turbulence model (Zero-EQ),(b) study the convective heat transfer coefficients at the external surfaces of different street canyon and building arrays,(c) demonstrate improved Zero-EQ and combined wall temperature and convective heat transfer coefficient to prove that this enable to accurately and quickly predict thermal environment in urban area,(d) investigate pollutant convective transport in uran areas. The detailed research content can be found as follows:This research provide the commonly used method for CFD simulation setup in urban area, including the choice of turbulence model, definition of numerical error, setup of computational zone, drawing computational grids and setup of computational boundary condition based on large amout of refrences and experiences. Finally, the classification of simplified CFD simulaton setup was built in order to provide the researchers some summery of theory and experience.The wind tunnel was selected to collect velocity data to derive improved the expression of turbulence visocistiy. The comparison with wind tunnel experiment was made. The results show that running Zero-EQ is60%faster than running MMK model and1/10of running LES. The Zero-EQ can relatively accurately predict the flow field around the buildings. Taking into account the limition for application in different case in the wind tunnel, this study then run two-equation turbulence model to predict velocity distribution around building arrays and obtained the expression (Zero-EQ2and Zero-EQ3) based on!! and local velocity magnitude. The three Zero-equaiton turbulence models were simulated to compare with the MMK model to analyze the accurancy in building arrays. The results show Zero-EQ2and Zero-EQ3can more accurately and quickly predict the flow field aournd building arrays.This research studied the convective heat transfer coefficients in different H/W of street canyon and λp of building arrays using CFD method, and derived different expressions for convective heat transfer in different building type, The wind tunnel made by previous research and field measurement were conducted to collect enough computational boundary conditions and validation data. The accurancy was indirectly proved that using combined convective heat transfer coefficient and wall temperature and also decreased computational grids. The Zero-EQ was used to predict thermal environment in street canyon and collect better data agreed with that of wind tunnel. Compared with RANS two equation turbulence model, it showed that the advantage of Zero-EQ in engineering field. The results also show the Zero-EQ cannot more accurately simulate buoyance flow. In addition, the convective heat transfer can be used for further study about energy simulation.The outcome which is improved Zero-EQ and convective heat transfer coefficient in this study were used to study pollutant distribution affected by thermal environment in the street canyon and building arrays. The RNG model was selected to investigate velocity, temperature and pollutant distribution under the condition of natural convection, combined convection and forced convection for different wall heated in street canyon, because of the limitation of Zero-EQ to simulate buoyancy flow. Moreover, only forced convection was selected to anlyze the pollutant distribution under the temperature difference (△T=0℃,10℃) between inlet temperature and wall temperature. The result shows the Zero-EQ can quickly and accurately predict the pollutant distribution. In the end, the ecological planning in Shouan twon was studied using Zero-EQ model. The thermal environment in old city area was firstly simulated on the basis of local weather condition. The velocity and temperature distribution around building were analyzed to provide some suggestions for palnning innew Shouan town. In the end, EnergyPlus was used to simulate the building energy consumption for a student dorm, so as to study the application of convective heat transfer coefficient when taking into account shielding effect.更多还原