Aerodynamic Parameters of Urban Building Arrays with Random Geometries
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- 作者：Sheikh Ahmad Zaki ; Aya Hagishima ; Jun Tanimoto and Naoki Ikegaya
- 关键词：Displacement height ; Drag coefficient ; Roughness length ; Urban building arrays ; Wind ; tunnel experiments
- 刊名：Boundary-Layer Meteorology
- 出版年：2011
- 出版时间：January 2011
- 年：2011
- 卷：138
- 期：1
- 页码：99-120
- 全文大小：1.1 MB
文摘
It is difficult to describe the flow characteristics within and above urban canopies using only geometrical parameters such as plan area index (λ p ) and frontal area index (λ f ) because urban surfaces comprise buildings with random layouts, shapes, and heights. Furthermore, two types of ‘randomness’ are associated with the geometry of building arrays: the randomness of element heights (vertical) and that of the rotation angles of each block (horizontal). In this study, wind-tunnel experiments were conducted on seven types of urban building arrays with various roughness packing densities to measure the bulk drag coefficient (C d ) and mean wind profile; aerodynamic parameters such as roughness length (z o ) and displacement height (d) were also estimated. The results are compared with previous results from regular arrays having neither ‘vertical’ nor ‘horizontal’ randomness. In vertical random arrays, the plot of C d and z o versus λ f exhibited a monotonic increase, and z o increased by a factor of almost two for λ f = 48–70 % . C d was strongly influenced by the standard deviation of the height of blocks (σ) when λ p ≥ 17 % , whereas C d was independent of σ when λ p = 7 % . In the case of horizontal random arrays, the plot of the estimated C d against λ f showed a peak. The effect of both vertical and horizontal randomness of the layout on aerodynamic parameters can be explained by the structure of the vortices around the blocks; the aspect ratio of the block is an appropriate index for the estimation of such features.