室外热环境分析中下垫面等效太阳辐射吸收系数的研究

发布时间：2018-04-03 06:44

  本文选题：室外热环境数值仿真　切入点：下垫面　出处：《华南理工大学》2013年硕士论文

【摘要】：在室外热环境分析中，正确描述下垫面对太阳辐射的吸收是一个重要前提，由于下垫面换热是集太阳辐射吸收、乔木树冠遮阳、含水表面蒸发冷却、空气对流传热和大气长波辐射的耦合换热过程，在利用大型商业CFD软件进行室外热环境数值解析时，对这种复杂换热过程的边界条件进行数值解析是非常困难，计算机时成几何级增长，收敛难度也大大增加。目前工程中常用建成区下垫面实测温度作为热环境分析的边界条件，对规划方案进行数值预测，虽然这种做法可以简化数值计算过程，但是建成区的下垫面铺装与规划方案只是一定程度的类似，计算结果误差较大。本文在下垫面热平衡方程的基础上，综合考虑下垫面水分蒸发散热和乔木树冠遮阳对下垫面太阳辐射吸收的影响，提出等效太阳辐射吸收系数，简化大型商业CFD软件中边界条件的设置，缩短计算机时，提高数值解析结果的工程可信度。 首先，本文介绍目前国内外下垫面换热边界条件研究现状，重点介绍大型商业CFD软件在模拟室外热环境的优势，以及在处理室外热环境时下垫面边界层设定遇到的问题，提出解决思路。其次，在传热与传湿控制方程的基础上，对透水地面、草地和植林地三种典型下垫面铺装方式的换热过程进行数值解析，推导下垫面温度和等效太阳辐射吸收系数的计算模型。第三，通过对下垫面逐时温度与实测温度的比较分析，验证下垫面温度计算模型的可靠性和准确性。分析表明，模拟值与实测值吻合较好，相关度在0.98以上，最大相对误差均在7%以内。第四，将等效太阳辐射吸收系数的计算值作为下垫面边界条件对太阳辐射吸收的等效转换，对对比分析的测试环境进行整体热环境数值仿真。分析表明，模拟值与实测值吻合较好，最大温度偏差在2℃以内，最大相对误差均在5%以内。最后，分析三种下垫面铺装方式的等效太阳辐射吸收系数的影响因素，得出提高草地叶面积密度，提高透水性下垫面的含湿量和缩小乔木间距使增大阴影率和增加乔木叶面积密度，能减少等效太阳辐射吸收系数，提高乔木对地面的阴影率对减少等效太阳辐射吸收系数效果更为显著。 等效太阳辐射吸收系数比较客观地描述下垫面蒸发冷却和乔木树冠遮阳的对室外热环境的影响，该系数的提出为工程界对小区规划方案的热环境进行快速分析提供了可能，，具有重要的工程应用价值。
[Abstract]:In the analysis of outdoor thermal environment, it is an important prerequisite to correctly describe the absorption of solar radiation from the underlying surface. Because the heat transfer of the underlying surface is the absorption of solar radiation, the canopy of the tree is shaded, and the surface of the water is evaporated and cooled.In the coupled heat transfer process of air convection and atmospheric long wave radiation, it is very difficult to analyze the boundary conditions of this complex heat transfer process by using commercial CFD software.Computer time into geometric level growth, convergence difficulty is also greatly increased.At present, the measured temperature of the underlying surface of the built area is used as the boundary condition for the thermal environment analysis, and the planning scheme is predicted numerically, although this method can simplify the process of numerical calculation.However, the underlying surfacing of the constructed area is only similar to the planning scheme to some extent, and the error of calculation results is large.Based on the heat balance equation of the underlying surface and considering the effects of water evaporation and canopy shading on the solar radiation absorption of the underlying surface, an equivalent solar radiation absorption coefficient is proposed in this paper.The setting of boundary conditions in large-scale commercial CFD software is simplified and the engineering reliability of numerical analysis results is improved when the computer is shortened.Firstly, this paper introduces the current situation of the research on the heat transfer boundary conditions of the underlying surface at home and abroad, and focuses on the advantages of the large-scale commercial CFD software in simulating the outdoor thermal environment, and the problems encountered in the setting of the underlying surface boundary layer when dealing with the outdoor thermal environment.The solution is put forward.Secondly, based on the governing equations of heat transfer and moisture transfer, the heat transfer process of three typical underlying surface paving modes, namely, permeable ground, grassland and planted forest land, is analyzed numerically, and the calculation model of underlying surface temperature and equivalent solar radiation absorption coefficient is derived.Thirdly, the reliability and accuracy of the model are verified by comparing the hourly temperature of the underlying surface with the measured temperature.The analysis shows that the simulated value is in good agreement with the measured value, the correlation degree is more than 0.98, and the maximum relative error is less than 7%.Fourthly, the calculated values of the equivalent solar radiation absorption coefficient are taken as the equivalent transformation of the underlying surface boundary conditions to the solar radiation absorption, and the overall thermal environment numerical simulation is carried out for the test environment compared and analyzed.The analysis shows that the simulated value is in good agreement with the measured value, the maximum temperature deviation is less than 2 鈩

本文编号：1704061