城市局部气候分区及其参数化条件下风环境模拟

Simulation on urban wind environment based on local climate zones and its parameterization

在改善城市空气污染和城市热岛研究时,城市风环境研究受到人们关注。利用计算流体力学(CFD)的方法直接对城市尺度风环境进行模拟,将是一种高效的研究方法。本文对局部气候分区及其参数特征进行分析,针对中国城市化建筑高大化、密集化的特点以及多孔介质模型对城市下垫面参数化的要求,提出基于局部气候分区及其参数进行城市风环境数值模拟的方法,并以西安市西咸新区的沣西新城为例进行初步探讨。对沣西新城的模拟结果显示了本文方法的可行性,并对该区域通风廊道建设进行分析。

Background, aim, and scope In the face of rapid industrialization and urbanization, China is confronted with growing contradictions among urban population, resources and environment. At present, China has become one of the most polluted regions in the world. The frequency, magnitude, and intensity of haze events have kept growing over China. Reasonable urban wind environment is crucial for mitigating air pollution and urban heat island effects. Materials and methods In study of urban wind environment, the computational fluid dynamic （CFD） method is a high-efficiency method. For urban scale wind environment simulation, physical model of urban canopy layer acts a key role in determining the accuracy of the simulated results. The local climate zones （LCZs） have been validated of advantages in characterization the urban canopy layer, by dividing the urban areas into blocks. Results In the current work, local climate zones and its parameterization are investigated, based on which a new method for urban wind environment simulation is proposed. Eight LCZs with different building types and seven LCZs with different land cover types are defined. Fengxi New Town a new development zone in Xi＇an, is divided into about 429 blocks. Each block has the characteristics of one or two LCZs. Characteristics of urbanization in China and the parameterization in porous medium models are considered in this newly proposed method. With this newly proposed method, wind environment in Fengxi New Town is studied. The designing on ventilation corridors in Fengxi New Town is also investigated. Discussion Results show grassland and farmland are the main LCZs in Fengxi New Town, which occupy 52% of the areas. Built areas of middle rise or high rise buildings are less, which only occupies about 10%. The wind environment in Fengxi New Town shows a ventilation corridor along the Weihe River, but no ventilation corridor along the Fenghe River. It seems the development of an ventilation corridor is heavily affected by the wind direction. Conclusions LCZs is a reasonable method to describe the urban canopy layer characteristics. The results show the practicability of the newly proposed method for urban wind simulation. Recommendations and perspectives Although there are two rivers in Fengxi New Town, but ventilation corridor is only developed over the Weihe River. It is recommended that in designing of ventilation corridor, the wind direction should be considered.