Abstract This study simulated the flow and near-field plume dispersion in an urban-like environment under unstable, neutral and stable atmospheric stratification using the steady Reynolds-averaged Navier-Stokes (RANS) methodology. First, a validation study for two trials of the Mock Urban Setting Test (MUST) experiments is performed to examine the predictive performance of the computational fluid dynamics (CFD) model, Fluidyn-PANACHE. The effects of atmospheric stability on the flow structure in street canyons under perpendicular incident flow conditions are investigated. In addition, the patterns of urban dispersion in different cases of stability are also analysed under perpendicular and oblique wind direction conditions. The results show that in the urban environment, the influence of atmospheric stability on the canyon vortex intensity, flow structure and plume dispersion is apparent; intense thermal turbulence enhances the vortex intensity and plume dilution in the street canyon under unstable conditions; when the atmospheric conditions are stable, the vertical profile of the streamwise velocity is significantly decreased by the obstacles, and the concentration level and spread of pollutants increase in the street canyon due to relatively weak turbulent motions; plume deflection within the obstacle array is noteworthy when the incident flow is oblique; in particular, the transport of the plume is basically independent of the wind direction very near the ground.

中文翻译：

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不同大气稳定条件下理想城区流场及污染物扩散数值模拟

摘要 本研究使用稳定雷诺平均纳维-斯托克斯 (RANS) 方法模拟了不稳定、中性和稳定大气分层下类似城市环境中的流动和近场羽流扩散。首先，对模拟城市环境测试 (MUST) 实验的两次试验进行了验证研究，以检查计算流体动力学 (CFD) 模型 Fluidyn-PANACHE 的预测性能。研究了大气稳定性对垂直入射流条件下街道峡谷中流动结构的影响。此外，还分析了垂直和倾斜风向条件下不同稳定性情况下的城市分散模式。结果表明，在城市环境中，大气稳定性对峡谷涡强度的影响，流动结构和羽流扩散明显；在不稳定条件下，强烈的热湍流增强了街道峡谷中的涡流强度和羽流稀释；当大气条件稳定时，由于障碍物的影响，流向速度的垂直剖面显着降低，由于湍流运动相对较弱，污染物在街道峡谷中的浓度水平和扩散增加；当入射流是倾斜的时，障碍物阵列内的羽流偏转是值得注意的；特别是，羽流的传输基本上与非常靠近地面的风向无关。障碍物使流向速度的垂直剖面显着降低，由于湍流运动相对较弱，污染物在街道峡谷中的浓度水平和扩散增加；当入射流是倾斜的时，障碍物阵列内的羽流偏转是值得注意的；特别是，羽流的传输基本上与非常靠近地面的风向无关。障碍物使流向速度的垂直剖面显着降低，由于湍流运动相对较弱，污染物在街道峡谷中的浓度水平和扩散增加；当入射流是倾斜的时，障碍物阵列内的羽流偏转是值得注意的；特别是，羽流的传输基本上与非常靠近地面的风向无关。