并列双方柱绕流的大涡模拟及频谱分析

应用二阶全展开ETG有限元离散格式与大涡模拟相结合的方法，对间距比为1.5情况下的并列双方柱绕流进行了数值模拟．由王小华、何钟怡提出的二阶全展开ETG有限元方法通过对N-S方程中的时变项进行Taylor展开，从而把时间导数用空间导数来代替，其作用相当于引入了人工粘性．计算得到了不同时刻的流线图，给出了两方柱的阻力系数、升力系数以及两对称点上流向速度随时间的变化历程，并采用谱分析的方法研究了对称边界条件下并列双方柱绕流的频谱对称性问题．为了消除初始条件的影响，在所取样本中去除了计算中初始段的数据，分别分析了阻力系数、升力系数以及两对称点上流向速度的频谱．结果表明:对称边界条件下，双方柱绕流运动参量的时域过程虽然是不对称的，但频域过程却是对称的．

Large Eddy Simulation and Spectrum Analysis of Flow Around Two Square Cylinders Arranged Side by Side

Large eddy simulation cooperated with the second order full extension ETG finite element method was applied to simulate the flow around two square cylinders arranged side by side at a spacing ratio of 1.5. The second order full extension ETG finite element method was developed by Wang and He. By means of Taylor expansion of terms containing time derivative, time derivative is replaced by space derivative. The function of it is equal to introducing an artificial viscosity term. The streamlines of the flow at different moments were obtained. The time history of drag coefficient, lift coefficient and the streamwise velocity on the symmetrical points were presented. Furthermore, the symmetrical problem of the frequency spectrum of flow around two square cylinders arranged side by side were studied by using the spectral analysis technology. The data obtained at the initial stage are excluded in order to avoid the influence of initial condition on the results. The power spectrums of drag coefficient, lift coefficient, the streamwise velocity on the symmetrical points were analyzed respectively. The results show that although the time domain process of dynamic parameters is non-symmetrical, the frequency domain process of them is symmetrical under the symmetrical boundary conditions.