Large Eddy Simulation Of Fluctuating Wind Field Of Atmospheric Boundary Layer Based On The Synthetic Fourier Method

With the emerging of super-high and long-span modern buildings,these wind sensitive buildings have received more and more attention.The computational wind engineering developed rapidly provides an effective method for the analysis of flow around buildings.As a hotspot of this area,the large-eddy simulation requires well-prepared fluctuating inflow condition to reproduce the realistic atmospheric boundary layer.At presen t,the synthetic Fourier methods have been widely used because the y are easy to implement with a high computing speed,but there still exist some deficiencies such that not all target turbulence characteristics can be strictly reproduced.Firstly,the thesis clarifies the basic concepts of turbulence characteristics and the applicability of the target turbulence characteristics using the synthetic Fourier method.The related parameters of four basic formulas based on the synthetic Fourier method proposed by Kraichnan et al,are investigated from six aspects: mean fluctuating wind speed,root mean square,wind velocity spectrum,time correlation,spatial correlation and randomness.The accuracy of the target turbulence characteristics is analyzed and some pre cautions in the application process are pointed out.The results show that the four methods mentioned above have not considered the realization of the target integration scale,and the spatial correlation of the generated fluctuating wind field can be appr oximated to the target value by trial calculation,obviously,it will need more computation.Aiming at eliminating the shortcomings of the current synthetic Fourier methods,the thesis proposed an improved synthetic method named as Correlation Improved Random Flow Generation(CIRFG)method.The target turbulence characteristics are determined by analyzing their features and feasibilities.Compared with the CDRFG(Consistent Discrete Random Inflow Generation)and the NSRFG(Narrow Spand Random Flow Generator)methods,it is verified that the improved method can accomplish more target turbulence characteristics and has a higher computational efficiency.Particularly,by unveiling the intrinsic mechanism between the parameters of the synthetic Fourier method and the target turbulence characteristics,the CIRFG method is capable of strictly satisfying the integral scale and the lateral spatial correlation coefficient of the longitudinal wind components.The large eddy simulation of CAARC(Commonwealth Advisory Aeronautical Research Council)benchmark model is carried out by using the fluctuating wind field generated by the CIRFG method as the inlet condition.Comparison with the results of wind tunnel experiments demonstrated that the CIRFG method has a high reasonable higher accuracy than the CDRFG and NSRFG methods.