Improvement,Verification And Application Of Numerical Turbulence Boundary Layer Generation Method Based On Harmonic Superposition Principle

The damage caused by the wind disaster to building structures is wide and the losses are large.Due to the continuous emergence of light and flexible high-rise buildings,higher requirements are placed on the wind resistance of high-rise building structures.Especially in the strong wind/typhoon area,wind load is a control load for the comfort and safety of super high-rise buildings.With the development of computer technology,numerical simulation?CFD?has gradually become a main research method of structural wind engineering in recent years.Large eddy simulation?LES?,as an unsteady numerical simulation method,is favored by researchers because it can accurately simulate the actual transient flow field.O ne of its key technologies is to generate accurate and efficient inflow turbulence.A new turbulence generation method is proposed based on an indepth discussion of the existing turbulence inlet generation method of LES,and it is applied to standard high-rise building models and actual engineering case analysis.The time history of inlet wind speed generated by the new method accords with the spatiotemporal correlation,and has high accuracy and fast efficiency.The simulated wind load is closer to the wind tunnel test results.The main content and conclusions of this paper are as follows:?1?This paper improved the method of narrow band synthesis random flow generation based on superposition of harmonics.And the improvements are as follows:1)Introduce a new time correlation parameter?₀ to consider the time correlation of the turbulent wind field,and choose an appropriate value of?₀ to satisfy the time correlation of actual turbulence,thereby achieving accurate simulation.2)In order to accurately calculate the energy of the wind speed energy spectrum,the integral expression of the wind speed spectrum is corrected by introducing the spectral energy correction parameter?_i,and an accurate expression of the spectral energy is proposed.The new turbulence inlet generation method?MNSRFG?can simulate the wind speed that more closely match the target value of the physical problem.And it can more accurately simulate the turbulent characteristics of the atmospheric boundary layer,which will help solve the problems that plague the accurate simulation of turbulent wind fields in the field of computational wind engineering.?2?Verification of modified narrow band synthesis random flow generation?MNSRFG?.The spectral characteristics and spatial-temporal correlation of the atmospheric numerical boundary layer constructed by this method are verified by a typical ABL numerical example,and at the same time,the influence of the introduced parameters is analyzed.The results show that the turbulence field generated by the new method satisfies the time correlation,spatial correlation and power spectrum characteristics of ABL turbulence field.After introducing the spectral energy correction parameter?_i,compared with the NSRFG method,the turbulence accuracy significantly improved.?3?The MNSRFG method is applied to the turb ulent flow around the standard high-rise building model?CAARC?in the field of wind engineering.Before conducting the calculation of wind flow around the building model,a simulation of a simple atmospheric boundary layer flow in an empty domain is performed first to determine whether the generated turbulent flow field by using MNSRFG method is consistent with the predetermined inflow wind characteristics.The improved method could increase significantly the accuracy of simulated turbulence intensity compared with NSRFG method.The simulation results before and after the improvements are compared with the wind tunnel test results to verify the reliability and accuracy of the improved method.The results show that MNSRFG method improves the accuracy of the wind pressure simulation on the C AARC model surface.Compared with the CAARC side elevation rms of wind pressure generated by the NSRFG method,the errors of rms of wind pressure coefficient are decreased from 18%?29%to 6%?12%?And the improved method decreased the errors of rms of based bend moment from 5.3%to 4.1%in along wind direction,5.6%to 1.3%in cross wind direction,respectively.Therefore,the improved MNSRFG method has higher accuracy,and the simulated wind load is closer to the wind tunnel test results.?4?The MNSRFG method is further applied to actual engineering cases-Guangzhou Hitachi Elevator Test Tower?268.8m?.Taking the cross-section super high-rise building with an aspect ratio of 12:1 as an engineering case,the MNSRFG method was used to simulate the wind load to calculate the wind-induced vibration response,and the results are in good agreement with the results of high frequency force balance?HFFB?wind tunnel test.In addition,some aerodynamic wind resistance measures?mainly opened ventilation slots and chamfered modification?were simulated on this project example.The simulation results show that for the cross-section super high-rise building,chamfering ca n effectively reduce the structural wind load;and the arrangement of wind caves can also effectively reduce the wind load,but the effect of reducing the cross wind load is far better than along wind direction.The based bend moment response decreases about 1.2%in along wind direction,12.5%in cross wind direction,respectively.Finally,the conclusions are presented and future work is briefly discussed.