Characteristics Of Mean Wind Speed Distributions And Wind Environment Assessment At Pedestrian-Level Height Around Super-Tall Buildings

Local strong wind caused by tall and super-tall buildings often makes it difficult for pedestrians to move,and even causes the occurrence of safety accidents such as pedestrians being blown down and injured.This is because the air flow is disturbed when passing through the building forming a strong acceleration of wind speed in the local area near the ground,which is not conducive to the comfort and safety of pedestrian activities.At present,a large number of wind-tunnel tests,CFD simulations and full-scale measurements have been carried out to study the characteristics of pedestrian-level wind around tall buildings.And most of these researches mainly focused on pedestrian-level wind environments around traditional symmetric tall buildings(under 200m height)such as square-and rectangular-plan buildings.The existing studies still have significant lack of the research on pedestrian-level wind distribution around super-tall buildings which higher than 200m.Especially,the flow around the super-tall buildings with untraditional configurations,such as the tapered-and helical plan and so on,is complex.Obviously the previous studies on pedestrian-level wind might be insufficient to assess the environmental conditions for urban areas around unconventionally shaped super-tall buildings.The relevant research is urgently needed.Accordingly,based on the wind tunnel experiments and theoretical analysis,this PhD thesis carries out a deep research mainly on pedestrian level wind distribution and wind environment assessment of super-tall buildings.The major contents and achievements are summarized as follows:1)A series of wind-tunnel tests were carried out to investigate the characteristics of pedestrian-level wind around square buildings with various dimensions,in particular,to examine the effects of building height,building width,building aspect ratio and approaching flow profile.Two different physical causes can be pointed out for speed-up phenomena of pedestrian-level wind from this study.One is Venturi Effect,and the other is Downwash Effect.It is found that for the buildings in boundary layer flow,the downwash effect on pedestrian level wind is more significant than Venturi effect.Besides,two types of downwash effect variations were found:one is due to change in flow pattern from 3D to 2D(Type 1)and the other is due to change in flow speed captured at around the front stagnation level(Type 2).2)Based on the experiment results and analysis of possible physical explanation of pedestrian level wind,i.e.Type 1 and Type 2 downwash effects,a series of new generic models for predicting the characteristic of pedestrian level wind around tall and super-tall building with square section are proposed herein.3)A series of wind-tunnel tests were carried out to investigate the pedestrian-level wind around 40 super-tall building models with various configurations including tapered models,corner-modified models,helical models,polygonal models,etc.The results of these tests have led to comprehensive discussions on pedestrian-level-wind characteristics of various super-tall building configurations under the condition of "same height and same volume".Some important configuration parameters effecting on pedestrian level wind such as corner modifications,twist angle of helical models,number of sides of building plan,projected width,etc.are recognized.It is found that the building without sharp corner shows the good behavior on pedestrian level wind environment.The projected building widths,especially in the lower part,affect significantly the pedestrian-level wind.By comparing all the test building models,the pedestrian level wind around circular model is the best,and that around the triangular model is the worst.4)Base on the wind speed data and Murakami criteria,the pedestrian wind environments around the square buildings with various geometric dimensions and 40 super-tall buildings with various configurations in Beijing area have been assessed to examine the effects of important parameters such as building dimensions,building configuration and building orientation on pedestrian wind environment.According to the high correlation between the maximum exceedance possibility and maximum speed-up ratio,some generic models are proposed to predict the maximum exceedance possibility around square buildings in Beijing area,which could be used to preliminarily determine the necessity of wind environmental assessment for square buildings with any dimensions.