Modeling and Simulation of Thermal Air Circulation above an Urbanized Area

摘要

A numerical model to represent the impact of urban buildings on airflow in meso'scale turbulence models is presented. In the model, the buildings are not explicitly resolved, but their effects on the grid-averaged variables are parameterized. An urbanized area is characterized by a horizontal building size, a street canyon width and a building density as a function of height. The improved, three-parametric E -ε- (θ~2){top}- turbulence model for the computation of the wind field, air temperature and pollutant dispersion was developed. The transport of momentum, heat and mass under density stratification is evaluated from the fully explicit anisotropic algebraic expressions. These expressions are derived based on the assumption of weak-equilibrium turbulence approach where transport effects on the stresses and heat fluxes are negligible. The heating processes at surfaces of buildings and ground are also modeled. The comparison of the computational results obtained with the present model and existing observational data and numerical models shows that the present model is capable of predicting the structure of turbulence in the urban canopy layer under density stratification and of obtaining high-resolution local wind fields. Numerical experiments with the new three-parametric model show that the behavior of the airflow in the urban canopy layer and above urbanized area is strongly affected by the existence of buildings and thermal stratification, including the urban heat island effect.