Esearch On Local Aerodynamic Strategy For Super-tall Buildings Based On Large-Eddy Simulation

Super-tall Buildings are typical wind-sensitive structures due to the light damping,long vibration period and high flexibility,which make wind loads become the dominant load for the safe and comfort design of the structure.The aerodynamic optimization is especially worthy for attention in the field of wind-resistance study of high-rise buildings.The reason for this is that modifying the global or local aerodynamic shape can reduce the wind effect of the structure,including wind loads and wind response,and it's less costly than structural and mechanical measures.Aerodynamic optimization is thereby one of important research issues in the field of wind-resistance study of high-rise buildings.In addition,it is possible to combine the aerodynamic optimization measures with the architectural design to achieve a win-win result for technology and art.In the present research,the numerical simulation,particularly LES techniques,is adopted as the main research tool,to study the wind loads and aerodynamic optimization for super-tall buildings.The main research contents of this paper are as follows:(1)First,numerical simulation of the turbulent wind field is studied based on RANS(Renolds-averaged Navier-Stokes)framework.Accurately modeling the neutral equilibrium atmospheric boundary layers(ABL)is a fundamental problem in the field of computational wind engineering(CWE),and it is a hot issue in recent years.A comprehensive and systematical summary on the theoretical research advances in this topic in recent years is given from four aspects first,which are the inflow boundary conditions,the turbulence model parameters,the additional source term and the wall function respectively,and a new set of model parameters and a general wall function based on the standard k-? turbulence model is then proposed.Numerical simulation model is built to model a simple boundary layer flow by using the CFD(computational fluid dynamics)method according to above four categories.Numerical results are compared and analyzed successively in detail.It is found that the imposed inflow boundary conditions deduced from the analytical solution of the turbulent kinetic energy k equation do not necessarily generate the equilibrium ABL,which depends on the mathematical model of the k profile to a large extent.Apart from the inflow boundary conditions,the turbulence model parameters and the wall function also have great effects on modeling the neutral equilibrium ABL.And adding source terms in the turbulence model equations can't effectively improve the self-maintenance of the velocity and the turbulent kinetic energy profiles throughout the whole domain without any obstacles.(2)Second,the NSRFG(Narrowband Synthetic Random Flow Generator)technique,which was the state of art inflow turbulence generator,is adopted to simulate the equilibrium turbulence ABL and flow around the CAARC standard high-rise building model.Influences from five aspects are entensively discussed,which are the inflow turbulence generator,the time step,the computation time,the truncated time and the computational mesh respectively.And the wind tunnel test data are adopted to validate the reliability of calculated along-wind response based on NSRFG.For the time step,it is suggested that the Courant number should be less than 2.5,without strictly satisfying the condition of the Courant number being no more than 1.Besides the inflow turbulence generator and the time step size,the computational time and the computational mesh also have great effects on modeling the turbulent equilibrium ABL and the blunt body flow.And the truncated time is not suggested for dealing with LES data.(3)Then the local aerodynamic optimization for super-tall rectangular building is studied by LES techniques from three aspects,and the wind pressure distribution,the base bending moment and the top displacement are systematically discussed.The results show that the across-wind response is more remarkable for higher buildings,meanwhile,the local aerodynamic strategy is more effective for them.Opening model at the four corners of the rectangular building with the height of 540 m can reduce the across-wind induced top displacement up to 57.7%.In addition,the best height adding the local aerodynamic strategy is about 0.6 times the building height,and opening model at four sides is the relatively most efficient measure,which can reduce the along-wind and across-wind induced top displacement by 34.5% and 36% respectively.(4)Finally aerodynamic optimazition strategies for a real super-tall building,the Shenzhen Kingkey Financial Tower(441.8m),are studied by the LES technique as a case study.The wind effects on four different models by placing different types of openings on the upper three refuge floors are numerically studied from three aspects,which are the flow field distribution,the base bending moment and the top displacement.The results show the all aerodynamic strategies could effectively reduce the strength of the shedding vortexes and hence the across-wind responses.Comparatively,full opening corner model by four sides is the most efficient measure,which can reduce the across-wind top displacement by about 26%.