Wind Environment Simulation In Urban Areas Under Typhoon Using A WRF Model Coupled With CFD Model

In recent years,the process of urbanization has been accelerating.Abundant construction of high-density and high-rise buildings has brought dramatic changes to the surface features but has highlighted a series of security issues.With global warming and the frequent occurrence of extreme weather,cities are particularly at risk of being affected by climate change.Unreasonable urban planning,to some extent,makes the characteristics of wind fields under extreme weather(e.g.typhoons)change within building clusters,which is more likely to lead to wind environment issues such as wind velocity intensively increasing,sharpchanging,and turbulent eddies around buildings,seriously endangering the pedestrians’ safety.It is therefore particularly important to avoid unreasonable architectural composition and to scientifically assess the impact of the urban wind environment on pedestrian safety.The simulation of urban wind fields within the atmospheric boundary layer using CFD(Computational Fluid Dynamic)techniques is one of the most important research methods available today,offering greater accuracy and reliability.However,the simulation of wind fields in the atmospheric boundary layer is a multi-scale problem.Changes in meteorological elements significantly impact the vortex intensity and flow structure of the flow field in urban building complexes.It is difficult to reflect the real wind field in the mesoscale range based on meteorological observations and empirical statistics,to establish the boundary conditions for CFD.Based on the above,this paper uses the WRF(Weather Research and Forecast)mesoscale meteorological model simulation coupled with CFD technology to carry out research.Firstly,the vector data corresponding to the geographic information and spatial patterns of urban buildings are extracted,and a mesoscale grid model is built from them.The WRF model was used to simulate the wind field of Typhoon Rumbia and was verified by comparing the data from meteorological stations.After validation,the wind field information over time is extracted from the WRF model simulation results and used as the boundary conditions and initial field for CFD simulations,and a unidirectional coupled WRF-CFD model is constructed to study the wind environment in the building complexes.A coupled WRF-CFD model is used in this paper,to simulate and study the complex wind field characteristics and typical areas of severe pedestrian wind environment in the Nanqiao area of Shanghai during Typhoon Rumbia.The results demonstrate that the coupled method is able to solve the cross-scale problem well and can realize a fine-grained simulation of the multi-scale flow field within a real building complex under the typhoon background field.The study shows that strong wind areas with wind speeds exceeding 15 m/s account for22.44% of the overall area of the study area,where wind speeds already affect pedestrian safety on foot.The wind hazard areas in the building include large building areas,ventilation corridor areas,and high-rise building areas.The most significant increase in wind speed is found at the corners of large buildings,where the maximum wind speed increases from 19.02m/s to 30.52 m/s within one hour.For high-rise buildings,the maximum wind speed on the windward side occurs at 10 m from the building wall and can reach 24 m/s.The further away from the building wall the wind speed value gradually decreases to below 15 m/s at 150 m from the leeward side of the building,while the windward side needs to be more than 200 m away before pedestrian control can be achieved.