Experimental Study And Numerical Simulations Of Aerodynamic Effects On A Tall Building Under Twisted Winds

With the rapid development of our country’s economy,the process of urbanization is accelerating.At the same time,advanced engineering construction technology is advancing rapidly,including the wide application of lightweight and high-strength materials,refined building structure design methods,and automated and intelligent building construction technology,Which makes more and more super high-rise buildings emerge all over the world.This type of building has the structural characteristics of higher,softer,lighter and low dampings,and are more sensitive to wind.Wind load is one of the main control loads in its structural design.Affected by the twisted force of the earth（Coriolis force）and the mountain effect,the wind direction will change along the height from the ground,which is also called twisted wind.However,the current load codes or standards of various countries assume that the horizontal wind direction angle in the atmospheric boundary layer does not change along the height,that is,straight-line wind,which lacks consideration of the influence of twisted wind that actually exists in engineering practice.Therefore,it is very necessary to carry out research on the wind effect and mechanism of super high-rise buildings under twisted wind.In order to solve the above problems,this paper based on the wind tunnel and CFD（Computational Fluid Dynamics）numerical simulation method.Firstly,The twisted wind inflows simulation was carried out..Secondly,the wind load characteristics of square super tall buildings under twisted wind are studied,and the influence mechanism of twisted wind is discussed based on the results of CFD numerical simulation.Finally,the wind load characteristics of super tall buildings with different side ratios under twisted wind inflows are studied.Specifically,the main work of this paper includes the following aspects:（1）The advantages and disadvantages of 4 existing models of twisted wind direction profile are summarized and compared,which are verified by wind tunnel.Based on the results,A vane system was designed.Combined with the traditional passive simulation facilites,the twisted wind inflows with certain wind characteristics was successfully simulated in the wind tunnel.The twisted wind inflows is also successfully simulated by two kinds of high fidelity unsteady CFD numerical simulation（Large Eddy Simulation,LES）methods: Direct simulation method and Artificial synthesis method.The accuracy of the wind inflows simulation is verified by the wind tunnel results.Based on the steady CFD numerical simulation（Reynolds Averaged Navier-Stokes,RANS）,some position parameters of the vane system are analyzed,the inflows movement mechanism under the action of the twieted is revealed,and the optimization criteria are put forward,which can provide some reference for the follow-up study of twisted wind inflows simulation.（2）Based on the rigid model wind tunnel and CFD numerical simulation method,the wind load characteristics of square super tall buildings are studied under twisted wind inflows and its corresponding conventional boundary layer wind inflows.The influence of twisted wind on wind pressure characteristics,layer force characteristics and base moment characteristics is clarified.The accuracy and validity of the wind load characteristics of CFD numerical simulation are verified by the wind tunnel results.Using CFD numerical simulation,the influence of total twisted angle of twisted wind on wind pressure characteristics of super tall buildings is explored,and the "effective total twisted angle" which can make the surface of super tall buildings produce obvious load asymmetry phenomenon is obtained.Finally,the mechanism of twisted wind is explained by POD（proper orthogonal decomposition）and flow field analysis.（3）Based on wind tunnel,the influence of side ratio on wind load characteristics of super tall buildings under twisted wind is studied,and the influence law of side ratio on wind pressure characteristics,layer force characteristics and base moment under twisted wind is clarified.Compared with the wind resistance performance,it provides a reference for the wind resistance design method of super tall buildings considering the side ratio under twisted wind.