Experimental Study On The Surrounding Wind Environment Of A Rectangular High-Rise Building With Oblique Winds

With the acceleration of China’s urbanization process,a large number of people poured into cities from the countryside,resulting in limited land resources of high intensity and high-density development and utilization exceeding the environmental carrying capacity."Looking for space from the sky" has become an inevitable trend in urban development;The record of the tallest building is constantly updated,high-rise and super-high-rise buildings have gradually developed into landmarks.Although the increase in building height improves the land plot ratio and alleviates the population problem to a certain extent,it also causes many wind environment problems.At present,the research on the wind environment of high-rise buildings mostly focuses on the distribution of the wind environment at the height of pedestrians in the building under vertical flow,and lacks a comprehensive understanding of the building space flow field under the condition of oblique flow;At the same time,most of these studies are based on time-averaged analysis,which can hardly reflect the transient flow process of the flow field around the building.In this study,the most representative rectangular high-rise building in the city was selected as the research object.Based on the wind tunnel experiment,the Phase Doppler Particle Analyzer is used to explore the time-averaged characteristics of the flow field at different heights around the building with oblique winds;At the same time,Particle Image Velocimetry is used to analyze the complex flow phenomena such as the evolution and shedding of the wake vortex in the flow around the building.This paper intends to reveal the formation of the wind environment around a rectangular high-rise building under the condition of oblique flow through the analysis of the time-averaged and transient wind environment characteristics.The following are the main conclusions of the paper:(1).The research on the vertical surface of the building shows that the high wind speed area at the top of the building is caused by the acceleration of the airflow at the top of the building caused by the updraft on the windward side of the building.The difference from the vertical flow is that under oblique flow,there is a band-shaped low wind speed area on the leeward side of the building,which is due to the existence of a pair of vortices moving in opposite directions on the leeward side;These vortices form recirculation on the leeward side of the building,and the boundary of the recirculation zone has the distribution characteristics of low time-averaged velocity and high turbulent intensity.(2).The research on the horizontal planes at different heights of the building shows that the flow fields at different heights are controlled by different airflows.The horizontal plane at the top of the building is affected by the conical vortex,the downflow,and the spanwise vortex;the horizontal plane in the middle of the building is mainly affected by the spanwise vortex;the bottom of the building is affected by the spanwise vortex and the bottom upwelling.The bottom of the building is the pedestrian area,the influence of the spanwise vortex and the bottom upflow will lead to the formation of backflow at the bottom of the building.In the case of low time-averaged wind velocity,it is easy to cause pollutants and heat accumulation,which is not conducive to the air quality and comfort of the pedestrian environment.(3)In the study of the transient flow characteristics around the building,it is found that the flow field characteristics of the windward side are consistent with the time-averaged research results as far as the vertical plane of the building is concerned.The vortex moving in the opposite direction on the leeward side of the building is not stable,which is mainly affected by the spanwise vortex around the building,the downflow at the top,and the upflow at the bottom.That is,when there is obvious airflow separation on the leeward side of the building,the vortex is affected by the downflow at the top,the upflow at the bottom and the spanwise vortex on the side of the building.There are conical vortices in the horizontal plane at the top of the building,the average size of the vortices is small and the shedding frequency is large;The horizontal plane in the middle of the building forms alternating shedding vortices,which form reflux.The average size of vortices is large and the shedding frequency is small.The horizontal plane at the bottom of the building is affected by different vortices,and the flow field distribution is complex.The development and shedding of vortices around buildings will cause damage to building structures and affect the wind environment of building pedestrian height.Thus affecting the safety of pedestrians.In this paper,the distribution characteristics of the spatial flow field around buildings and the wind environment at different heights under oblique winds are studied.The research results can provide a certain theoretical basis for urban building layout,pedestrian wind environment prediction,pollutant control,and so on.