边界入流风场扰动对模拟城市大气扩散的影响

Influence of boundary inflow wind fluctuation on simulated urban atmospheric diffusion

借助计算流体动力学(CFD)模式Fluent分析中性层结下边界入流风场(即风速和风向)扰动对地面点源释放情景下城市大气扩散过程的影响,其中边界入流条件以风速和湍流动能廓线的形式给出.研究发现CFD模式能够合理刻画实际城市中的特征流型(如涡旋,峡谷效应等),而且模拟的风速、风向和湍流动能均与观测数据吻合较好.敏感性试验结果表明,城区内的流场和湍流以及与之密切相关的污染物空间分布对边界入流风速和风向的扰动十分敏感.而这可能是造成已有研究中浓度模拟值与观测值不一致的主要原因之一.因此,在模拟城市大气扩散过程时应当考虑边界入流风场不确定性对模拟结果的影响.

The impact of the inflow wind fluctuation(i.e.wind velocity and wind speed)on the urban pollutant dispersionfrom a point source released at ground level under neutral stratification was analyzed using the computational fluiddynamics(CFD)model Fluent,where the boundary inflow conditions were provided in the form of wind velocity andturbulence profiles.Results suggested that the CFD model could reproduce the characteristic flow pattern(e.g.vortex,channeling,and so on)observed in actual urban environment,and the simulated wind velocity,wind direction andturbulence kinetic energy were in good agreement with observations.The results from a set of sensitivity experimentsshowed that the flow field and turbulent kinetic energy as well as the spatial distribution of pollutants in the urban areawere very sensitive to the fluctuation of inflow wind speed and wind direction.This may be one of the main reasons forthe inconsistency between the observed and the simulated concentrations in previous studies.Therefore,the uncertainty ofboundary inflow should be considered in future simulation studies on urban atmospheric diffusion.