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

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.