Large Eddy Simulation Of Local Aerodynamic Wind Resistance Strategy Of Super-tall Buildings With High Aspect-ratio

Wind load is the controlling load for the structural design of super high-rise buildings in typhoon prone areas.Aerodynamic shape optimization is a common method to reduce the wind load and wind-induced response on such structures.Its main purpose is to improve the wind resistance performance of super high-rise buildings by changing their aerodynamic shape.Aerodynamic shape optimization measures include overall strategy and local strategy.Generally,when the architectural design scheme has been determined,it is not allowed to modify the architectural shape greatly,so the local aerodynamic optimization strategy is more easily accepted by designers.With the development of computer technology and numerical algorithm,CFD(Computational Fluid Dynamics)numerical simulation technology is becoming more and more mature.It has become an indispensable research method in structural wind engineering besides wind tunnel test,and plays an important role in wind resistance design of building structure.In this paper,large eddy simulation(LES)and modified narrow band synthesis random flow generation(MNSRFG)are used to study the local aerodynamic wind resistance measures of a super high-rise building with large aspect ratio(9:1).The main contents and conclusions are as follows:(1)Firstly,the applicability of the improved MNSRFG method proposed by research group in this study is verified,and the appropriate calculation parameters are given.The large eddy simulation(LES)of CAARC standard high-rise building model,which is commonly used in the field of wind engineering,is studied and compared with the wind tunnel test results.The results show that the surface wind pressure coefficient,the power spectral density of the base moment and the wind-induced response of the model calculated by the improved MNSRFG method have higher accuracy,which are in good agreement with the experimental results.The relative error of the fluctuating wind pressure coefficient on the side of the standard model is reduced from 16.3%～26.8%to 7.2%～14.6%,and the relative error of the root mean square base moment coefficient along the wind direction and across the wind direction is reduced from7.9%and 12.7%to 3.2%and 3.4%respectively.In addition,according to the simulation results of different calculation time,it is suggested that when LES research is carried out on high-rise building structure,the total simulation time should be converted to the actual sampling time,which should be kept at more than 10 minutes,so as to meet the requirements of the code and obtain more accurate numerical results.(2)Then,based on the square section super high-rise building with height to width ratio of 9:1 and prototype height of 546m,rectangular openings are set along the height direction as local aerodynamic measures.A total of 10 opening conditions including the closed model are designed,and the LES numerical simulation is carried out by using the modified narrow band synthesis random flow generation(MNSRFG).By comparing the wind pressure distribution on the surface of the model,the power spectrum of the base moment coefficient and the wind-induced response of the structure,the effect of each opening condition is evaluated.The results show that the local penetration opening at 0.69H(H is the height of the building)is the best aerodynamic optimization scheme,which can reduce the aerodynamic effect to the greatest extent,and the peak base moment response of along-wind is reduced by 10.39GN·m,the reduction is about 22.96%,and the peak base moment response of across-wind is reduced by68.55GN·m,the reduction is about 31.97%.Compared with the fully enclosed scheme,the fluctuating displacement at the top of across-wind is reduced from 1.35m to 0.92m,and the acceleration is reduced from 0.402m/s~2 to 0.268m/s~2,both of which are reduced by more than30%.Therefore,it can be seen that the opening at 0.69 times the height of the structure has a better vibration reduction effect.(3)Finally,taking the square section super high-rise building as the benchmark,considering the corner opening treatment(local aerodynamic measures)in the upper,middle upper and lower parts of the building,the same numerical simulation method is used to study it.In order to evaluate the overall aerodynamic performance of different opening schemes,the influence of corner opening at different heights on the power spectrum of base moment coefficient,peak base moment response,top displacement and top acceleration is analyzed.The results show that the effect of corner opening in the middle and upper part of the building(0.65H)is relatively good,which can significantly reduce the aerodynamic bending moment spectrum energy in the downwind direction and crosswind direction,especially crosswind direction.Compared with the fully enclosed scheme,the peak base moment responses of along-wind and across-wind are reduced by 6.15GN·m and 37.82GN·m respectively,the corresponding reduction are 13.76%and 17.97%respectively.For the top displacement,when the middle and upper parts are open,the downwind displacement(average part and fluctuating part)can be reduced by 0.041m,and the crosswind fluctuating displacement can be reduced by 0.235m,both of which can be reduced by more than 13%.In the aspect of improving human comfort,the middle and upper corner opening scheme can slow down the peak acceleration response of about 17.22%in cross wind direction,and the effect can not be ignored.The above results can provide reference for wind resistance optimization of super high-rise buildings of the same order.