Effect of vegetative canopy architecture on vertical transport of massless particles
Effect of vegetative canopy architecture on vertical transport of massless particles
复制标题
DOI：
10.1016/j.atmosenv.2014.06.058
复制
发表时间：
2014-10-01
影响因子：
5
通讯作者：
Mahaffee, Walter F.
中科院分区：
文献类型：
--
作者：
Bailey, Brian N.;Stoll, Rob;Mahaffee, Walter F.
将具有重复行结构的近似分解非均质植被冠层的大涡模拟与“等效”均质模拟进行比较，以探索冠层总密度和水平非均质性如何影响非沉积无质量流体包裹的垂直输送。采用拉格朗日方法量化粒子色散。粒子运动的子网格分量用Langevin方程建模，该方程与一种新的半隐式格式相结合，成功地最小化了异常轨迹。在控制流氓轨迹的情况下，子网格模型对平均统计数据的影响可以忽略不计。分析表明，在冠层上方，冠层密度和非均质性对颗粒浓度和垂直通量的平均分布影响较小。然而，随着冠层密度的增加，颗粒滞留时间呈线性增加，释放高度对冠层逃逸的重要性增加。粒子持续垂直运动的平均时间不遵循这种单调趋势。对于足够稠密的冠层，持续垂直运动的时间尺度随冠层密度的减小而增大，与混合层尺度一致。随着林壁剪力的显著增强，持久性随着冠层密度的减小而减小。冠层异质性对停留时间和持续时间的影响与弥散通量的强度密切相关。冠层非均质性降低了粒子逃离冠层的平均时间，也降低了粒子垂直运动的相干性。(C) 2014 Elsevier Ltd.版权所有。
Large-eddy simulations of approximately resolved heterogeneous vegetative canopies with repeating row structure were compared to 'equivalent' homogeneous simulations to explore how overall canopy density and horizontal heterogeneity influence the vertical transport of non-depositing massless fluid parcels. A Lagrangian approach was used to quantify particle dispersion. The subgrid component of particle motion was modeled with a Langevin equation that was integrated with a new semi-implicit scheme that successfully minimized rogue trajectories. With rogue trajectories controlled, the subgrid model had a negligible impact on average statistics. Analysis suggested that above the canopy top, canopy density and heterogeneity had a minor effect on mean profiles of particle concentration and vertical flux. However, increasing canopy density resulted in a linear increase in particle residence time, and increased the importance of release height on canopy escape. The average time of persistent vertical particle motions did not follow this monotonic trend. For sufficiently dense canopies, the time scale of persistent vertical motions increased with decreasing canopy density in agreement with mixing-layer scaling. As wall shear became significant, a transition was observed in which persistence decreased with decreasing canopy density. The effect of canopy heterogeneity on residence time and persistence was well correlated with the strength of dispersive fluxes. Canopy heterogeneity decreased the average time for a particle to escape the canopy, and also reduced the coherence of vertical particle motions. (C) 2014 Elsevier Ltd. All rights reserved.