Wind tunnel experiments about transfer coefficient in urban surfaces and modeling of city structure.

城市对流热流模拟是热岛研究中的重要问题之一。本文利用我们首次提出的“蒸发技术”，研究了城市峡谷内对流换热系数的分布。与类似的热通量实验相比，该方法的优点是可以精确地测量对流通量。此外，我们还可以很容易地限制任意表面甚至表面内部的通量。本研究的主要内容是峡谷几何形状对三维立方体阵列的影响。测量了不同密度下对流换热系数的垂直分布，并考察了对流换热系数随风向的变化。同一曲面内系数的变化是不可忽略的，也就是说，如果假设所有位置都是恒定值，在某些情况下会导致相当大的误差。另一个问题是屋面形状对对流换热系数的影响。试验采用了山形屋面(倾角从平到65.4度)的二维模型。虽然这些周期性规则排列的实验为城市结构的建模提供了基础信息，但我们必须检验这种简化的排列是否能代表实际的城市。因此，我们还利用相同的水分蒸发技术测量了实际存在的城市模型沿街道的分布。同一条街道内各点之间差异显著，最大值超过最小值的两倍。由于对流换热系数与风速或扩散能力密切相关，因此可以认为这些结果也代表了各个位置的通风量。

The modeling of convective heat flux in urban area is one of the important problems in heat island study. In this paper, the distribution of convective transfer coefficient within urban canyon is investigated using our originally devised "water evaporation technique". The merit of this technique is to measure the convective flux precisely, in comparison with similar experiments about heat flux. Besides, we can easily restrict the flux in an arbitrary surface or even the portion within the surface.The main topic in this study is the effect of canyon geometry about three-dimensional cubic array. The vertical distributions of convective transfer coefficient were measured in various densities and its change due to wind direction was also examined. The variation of coefficient within same surface is not negligible, that means, if constant value assumed for all position it leads to considerable error in some case. Another topic is the effect of roof shape on convective transfer coefficient. The two-dimensional models with gable roof (inclination from flat to 65.4 degree) were used in experiments. The distributions of coefficient were revealed in all kind of model surface and street surface between models.Though these experiments about cyclic regular arrangement give fundamental information for modeling of urban structure, we have to check whether such a simplified arrangement is considered as a representative of actual city. Therefore, we also measure the distribution along a street of real existed city model using same water evaporation technique. The difference among points within the same street is remarkable, and maximum value exceed twice of minimum point. As convective transfer coefficient is closely related with wind speed or diffusion ability, it can be considered that these results are also representative of ventilation rate in each position.