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中文核心期刊

海岸城市上空热力内边界层的基本特征

A NUMERICAL STUDY ON THERMAL INTERNAL BOUNDARY LAYER OVER A COASTAL CITY

  • 摘要: 海岸热力内边界层内大气在热力驱动下产生垂向对流运动,对海岸带的大气运动规律产生深刻的影响.在海岸城市地区,受城市冠层复杂结构的影响,热力内边界层呈现诸多独特的性质.采用大涡模拟的方法,研究了海岸城市热力内边界层内的流动特征.将海岸城市建筑物拟形为一系列有序排列的立方体块,并基于浸入边界方法考虑其对大气流动的影响.和常见的区域尺度数值研究中将城市下垫面假设为均质属性平面的方法相比,模拟结果的精度明显提高,海岸热力内边界层内各种尺度的动力过程也能在一定程度上得以描述.模拟计算了海岸城市热力内边界层、中性海岸城市边界层和开阔的自然海岸热力内边界层共3种情况,对比研究了城市摩阻和海岸热力作用对海岸城市上空大气运动的影响.研究结果表明:在空间上,边界层中各紊流特征量均在街谷尺度呈现出有规律而非均匀分布的特点;在强度上,热力作用与城市构筑物的摩阻作用相互促进,使得紊流强度显著提升并大于两种作用线性叠加的结果.此外,还发现有城市冠层海岸的热力内边界层发展远快于相同热力条件下的自然海岸带,边界层的发展规律也有显著的不同.

     

    Abstract: In the coastal thermal internal boundary layer is very common, and the warmed air becomes unstable to induce a vertical advection of the air mass.Over a coastal city, the atmospheric flow is strongly affected by the complex morphology of the city, which is an alternation of the street canyon and the building.This leads to some special features of the coastal thermal internal boundary layer.A large-eddy simulation is carried out to study the thermal internal boundary layer flow over a coastal city in this study.The buildings in coastal cities are modelled as boxes with given geometry and known thermal properties.The immersed boundary method is used to represent the resistance of the buildings on the air flow.The numerical model thus captures more details of the coastal city as compared with the conventional regional models in which urban canopy is considered as the surface with a uniform property.Three cases are considered in the present study for a comparative study of the influence of urban resistance and land heating on the atmospheric flow.The computational results show that the spatial variation of the turbulence quantities is regular in a scale of the buildings. It is also demonstrated that the thermal buoyancy and the strong shearing effects interact with each other to intensify the turbulence in the boundary layer.Compared with the natural coast thermal boundary layer under the same thermal conditions, thermal internal boundary layer over a coastal city develops much faster.

     

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