城市建筑物动力冠层方案的引入及应用研究

Study on the incorporation and application of the aerodynamicalurban canopy scheme

  • 摘要: 文中将建筑物动力冠层方案引入到城市边界层精细模式中,该方案描叙了城市地区建筑物对气流的拖曳作用以及建筑物形态对城市地区湍流活动动量输送的影响。采用建筑物拖曳法和建筑物动力冠层方案两种不同建筑物动力学处理方法对北京地区东南部进行模拟,通过城市地区水平风速的模拟结果与自动气象站实测资料对比发现模拟结果与实测相当吻合,建筑物动力冠层方案的引入能够更好地实施对城市地区的水平风速分布的数值模拟。分别采用建筑物拖曳法与建筑物动力冠层方案对一个实际小规模城市进行模拟试验,分析表明引入建筑物动力冠层方案可以模拟出小规模城市地区水平风速偏低的现象;还可以模拟出城市地区建筑物动力作用对湍流活动的影响;对湍流动能模拟结果表明比较符合实际分布情形。采用建筑物动力冠层方案对小规模城市地区建筑物高度变化对城市地区的流场及湍流活动的影响进行模拟分析,结果表明:城市地区建筑物高度增加,风速变小,但是高大建筑物底部风速略高于低矮建筑物底部;城市地区大气湍能增加,高大建筑物底部湍能较小,冠层高度内湍能随高度增加而增加;同时城市地区的垂直扩散系数也随建筑物高度增加而增加;城市地区污染物排放高度处污染物浓度较低,下游乡村地区地面污染物浓度较低,但高空污染物 浓度却较高。

     

    Abstract: An aerodynamical urban canopy scheme is incorporated into the fine town boundary layer model. The scheme contains drag effect of urban buildings on flow and effect of building morphology on urban turbulent activity and momentum transfer. The incorporated model is evaluated by simulation results of two different building aerodynamical scheme in southeast region of Beijing area, which are building drag scheme and aerodynamical urban canopy scheme. The conclusions are drawn by the comparisons between the simulation results of the wind speed and the observations of the automatic weather stations in the urban areas: the simulated results of incorporated model are more in reasonable agreement with the observations than that of building drag scheme, and the diurnal trend of that is more agreement with observations. The model incorporated with the aerodynamical urban canopy scheme is better to simulate the wind field on the urban areas.The conclusions are drawn by the comparisons between the simulation results of the building drag scheme and the aerodynamical urban canopy scheme in a real town: the simulated wind speed with the aerodynamical canopy scheme on the town areas is always lower than that on the surrounding rural areas, but that with the other scheme is not so. The simulated results describe the dynamical effect of the buildings on the turbulent activity, and the simulated turbulent kinetic energy distribution is consistent with the real distribution.The effect of the building height variation in the town on the wind field and turbulence is also simulated, and the results are as followings: the increase of the building height results in the decrease of the horizontal wind speed on the town areas, and the wind speed at the bottom of the higher building is larger than that of the lower building. The turbulent kinetic energy on the town areas ascends, that in the bottom of the high building is lower and ascends with the height in the canopy layer. The vertical diffusion coefficient increases as the building height ascends. The pollution concentration on the town areas with higher buildings is lower on the emission level, and that is lower on the surface and is higher on the upper level of the downstream rural areas.

     

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