Processes controlling atmospheric dispersion through city centres
Processes controlling atmospheric dispersion through city centres
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控制通过城市中心的大气扩散的过程
DOI：
10.1017/jfm.2014.661
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发表时间：
2014
影响因子：
3.7
通讯作者：
Belcher S
中科院分区：
文献类型：
--
作者：
Belcher S
我们开发了一个基于过程的模型，用于在市中心建筑物周围的湍流中分散被动标量。街道网络模型基于将街道和交叉口的空域划分为多个盒子，其中湍流使空气充分混合。然后，通过街道和交叉路口箱网络的平均流平流调节进一步的横向扩散。同时，垂直方向的湍流混合将标量从街道和交叉口转移到建筑物上方的湍流边界层中。当几何形状规则时，街道网络模型具有解析解，该解描述单个源的近场顺风浓度变化，其中大部分标量位于屋顶水平以下。该分析解决方案的强大之处在于，它演示了如何仅通过三个参数来确定浓度。羽流方向参数描述了街道交叉口标量的分支，因此确定了羽流中心线的方向，该方向可能与屋顶上方的风向有很大不同。传输参数决定了大部分标量被转移到屋顶上方的大气边界层并且传统大气湍流成为主要混合过程之前行进的距离。最后，标准化源强度会乘以这种浓度模式。在经过大量交叉点后，该解析解收敛于高斯羽流，为先前开发高斯羽流模型经验拟合的研究提供了理论依据。该解析解与非常高分辨率的模拟和风洞实验相比较，尽管先前被释放到屋顶上方边界层的标量的重新夹带（在解析解中没有考虑到）已被证明成为距离源进一步顺风的一个重要过程。
We develop a process-based model for the dispersion of a passive scalar in the turbulent flow around the buildings of a city centre. The street network model is based on dividing the airspace of the streets and intersections into boxes, within which the turbulence renders the air well mixed. Mean flow advection through the network of street and intersection boxes then mediates further lateral dispersion. At the same time turbulent mixing in the vertical detrains scalar from the streets and intersections into the turbulent boundary layer above the buildings. When the geometry is regular, the street network model has an analytical solution that describes the variation in concentration in a near-field downwind of a single source, where the majority of scalar lies below roof level. The power of the analytical solution is that it demonstrates how the concentration is determined by only three parameters. The plume direction parameter describes the branching of scalar at the street intersections and hence determines the direction of the plume centreline, which may be very different from the above-roof wind direction. The transmission parameter determines the distance travelled before the majority of scalar is detrained into the atmospheric boundary layer above roof level and conventional atmospheric turbulence takes over as the dominant mixing process. Finally, a normalised source strength multiplies this pattern of concentration. This analytical solution converges to a Gaussian plume after a large number of intersections have been traversed, providing theoretical justification for previous studies that have developed empirical fits to Gaussian plume models. The analytical solution is shown to compare well with very high-resolution simulations and with wind tunnel experiments, although re-entrainment of scalar previously detrained into the boundary layer above roofs, which is not accounted for in the analytical solution, is shown to become an important process further downwind from the source.
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