Simulating Dispersion in the Evening-Transition Boundary Layer
Simulating Dispersion in the Evening-Transition Boundary Layer
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DOI：
10.1007/s10546-014-9960-0
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发表时间：
2014-08
影响因子：
4.3
通讯作者：
Alexander C. Taylor;R. Beare;D. Thomson
中科院分区：
文献类型：
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作者：
Alexander C. Taylor;R. Beare;D. Thomson
我们调查的扩散在均匀过渡边界层使用大涡模拟（LES）。在LES中，粒子模型跟踪污染物的路径使用的组合的解决流速和随机位移模型来表示亚网格尺度运动。LES被迫与突然关闭的表面热通量，也是一个更渐进的观察到的演变。大涡模拟显示了过渡前对流边界层中近地表释放的羽流的“放样”;它还显示了过渡后近地表稳定边界层和上方残留层中释放的后续“捕获”。由于缺乏观测的污染扩散在傍晚过渡，LES证明是一个有用的参考。然后，我们使用LES测试和改进的一维拉格朗日随机模型（LSM），如经常用于实际的分散研究。这里使用的LSM包括时变和偏斜湍流统计。它是被迫与垂直速度方差，偏度和耗散的LES颗粒释放在不同的高度和时间在傍晚过渡。的LSM羽蔓延显着大于那些从LES在过渡后稳定的边界层捕获制度。因此，来自LES的强迫不足以约束羽流的演变，需要包括显着的分层效应。在所谓的修正的LSM中，包括对垂直速度方差的校正，以表示稳定层结的影响和随之而来的波浪状运动的存在。改进后的LSM显示出改进的捕获后过渡稳定的边界层中的颗粒。
We investigate dispersion in the evening-transition boundary layer using large-eddy simulation (LES). In the LES, a particle model traces pollutant paths using a combination of the resolved flow velocities and a random displacement model to represent subgrid-scale motions. The LES is forced with both a sudden switch-off of the surface heat flux and also a more gradual observed evolution. The LES shows ‘lofting’ of plumes from near-surface releases in the pre-transition convective boundary layer; it also shows the subsequent ‘trapping’ of releases in the post-transition near-surface stable boundary layer and residual layer above. Given the paucity of observations for pollution dispersion in evening transitions, the LES proves a useful reference. We then use the LES to test and improve a one-dimensional Lagrangian Stochastic Model (LSM) such as is often used in practical dispersion studies. The LSM used here includes both time-varying and skewed turbulence statistics. It is forced with the vertical velocity variance, skewness and dissipation from the LES for particle releases at various heights and times in the evening transition. The LSM plume spreads are significantly larger than those from the LES in the post-transition stable boundary-layer trapping regime. The forcing from the LES was thus insufficient to constrain the plume evolution, and inclusion of the significant stratification effects was required. In the so-called modified LSM, a correction to the vertical velocity variance was included to represent the effect of stable stratification and the consequent presence of wave-like motions. The modified LSM shows improved trapping of particles in the post-transition stable boundary layer.