基于零方程湍流模型的非等温城市区域热环境的模拟研究

发布时间：2018-07-08 08:33

本文选题：城市热环境 + CFD模拟设定　；参考：《西南交通大学》2013年博士论文

【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。
[Abstract]:In the past two decades , most of the researches at home and abroad use RANS two - equation turbulence model and LES model to study the urban regional environment . Because of the complexity of urban regional environment and the large spatial scale , the main research contents of this paper are as follows : ( a ) the research methods of urban wind - thermal environment , the CFD simulation technology of urban environment , the surface - facing flow heat transfer coefficient of the building and the effect of convective heat transfer in urban area .

Through studying a large number of references and summing up the long - term CFD calculation experience , this paper presents a common setting method for the CFD simulation of urban area environment , including the selection of turbulence model , the determination of numerical error , the setting of calculation area , the delimitation of calculation grid , and the setting of calculation boundary conditions .

The results show that Zero - EQ is more than 60 % faster than MMK turbulence model , and it is used to predict the distribution of flow field around multiple buildings . The results show that Zero - EQ can predict the distribution of flow field around multiple buildings .

In this paper , the convective heat transfer coefficient of outdoor surfaces of different urban street heights ( H / W ) and different plane area densities ( 位p ) is studied by CFD simulation method . The expressions of convective heat transfer coefficient under different building distribution conditions are derived , and data of wind tunnel experiment data and field test ( a student apartment in Penn State University ) are selected to obtain enough computational boundary conditions and verification data , so as to reduce the grid of the calculation area , and the accuracy of the convective heat transfer coefficient is indirectly verified by setting the convection heat transfer coefficient and the temperature boundary as the wall surface calculation conditions ;
By using the zero equation turbulence model to calculate the thermal environment of the urban street valley , the data with good agreement with the wind tunnel experiment is obtained , which is twice as fast as the turbulence model of the RANS equation , which proves the advantages of the zero equation turbulence model for the prediction of buoyancy flow . In addition , the expression of the convection heat transfer coefficient calculated in this study can provide enough research basis for the future energy consumption simulation study .

In this paper , the effects of thermal environment on pollutant concentration in two - dimensional urban street and three - dimensional buildings are studied by using the above research results : optimized zero equation turbulence model and convection heat transfer coefficient of the outer surface of buildings .
【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：X16;TU119.4

【参考文献】