用格子Boltzmann方法数值模拟混合层中旋涡的合并过程

Numerical simulation of vortex merging in mixing layer using lattice Boltzmann method

用格子Boltzmann方法计算混合层中的流动问题。在流场的入口处加不同频率、振幅和相位的小扰动,观察混合层中旋涡的演进机理,模拟二维混合层中旋涡合并现象。在基本扰动波的基础上,又加入频率为基本波频率一半的亚谐波,得到了两个涡合并的计算结果,当加入的亚谐波频率为基本波频率的三分之一时,得到了三个涡合并的计算结果。这些计算结果与已有文献的结果基本一致,显示用格子Boltzmann方法模拟混合层问题是可行的。

The evolution of time-developing mixing layer is simulated numerically using the lattice Boltzmann method. In the inlet of the computational domain the velocity perturbation of various of frequencies, amplitudes and phases is applied to investigate the evolution of the vortexes and simulate the mergence of the vortexes in the two-dimensional mixing layer. If the perturbation is composed of a basic wave, and a sub harmonic wave with half frequency of the basic wave, the two-vortex mergence was found. If the frequency of the sub harmonic wave is 1/3 value of the basic wave, the three-vortex mergence appears. The results of large-scale vortex dynamics are visualized by means of isovorticity contours plots. It is seen that the vortex merging behavior in the mixing layers is determined by the subharmonics of the perturbation, and can be controlled by imposing multi-harmonics and changing their phase differences. The computational results are agreed with those of available literatures. It is shown that lattice Boltzmann method can be used for simulating the mixing layer and vortex mergence.