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

城市对流热通量的数值模拟是城市热岛研究中的重要问题之一。本文利用我们独创的“水分蒸发技术”研究了城市峡谷内对流输送系数的分布。与类似的热通量实验相比，该技术的优点是可以精确地测量对流通量。此外，我们可以很容易地将通量限制在一个任意的表面，甚至表面内的部分。本研究的主要议题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输送系数的垂直分布，并分析了其随风向的变化。同一曲面内的系数变化是不可忽略的，这意味着，如果假定所有位置都为常数，则在某些情况下会导致相当大的误差。另一个主题是屋顶形状对对流传递系数的影响。实验中使用的是带有人字形屋顶（从平面倾斜到65.4度）的二维模型。虽然这些关于循环规则排列的实验为城市结构的建模提供了基础信息，但我们必须检查这种简化的排列是否被认为是实际城市的代表。因此，我们也用同样的水分蒸发技术测量了真实的城市模型的沿着街道的分布。同一条街道内各点之间的差异显著，最大值超过最小值的两倍。由于对流传递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每个位置的通风量。

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.