模型预混燃烧室线性稳定性分析

Linear stability analysis of modal premixed combustor

针对钝体火焰稳定器结构的模型预混燃烧室进行了线性稳定性分析.利用COMSOL Multiphysics软件求解了三维Helmoholtz方程,方程的源项为耦合指数-延迟时间模型.对模型预混燃烧室进行非定常计算得到了化学反应速率的周期性变化,确定了非定常热释放发生在火焰的尖端.由压力和温度信号的相位差得到了当量比为0.72,0.8,0.88,0.97四个工况的延迟时间,分别为0.6,0.3,0.9,0.6ms.线性稳定性分析得到了模型预混燃烧室系统纵向模态频率的实部和虚部,当虚部为负数时表示线性不稳定.结果显示:系统的前5阶纵向模态中,2~4阶是线性不稳定的.其中3阶纵向模态的虚部绝对值最大,它的物理意义是对小扰动的增长率最大.因此在有扰动时,3阶纵向模态最有可能线性失稳,产生燃烧不稳定性现象.

Linear stability analysis was conducted in modal premixed combustor with bluff body flame holder. The software COMSOL Multiphysics was used to solve the three- dimensional Helmoholtz equation. The time lag model was the source term of equation. The periodic change of chemical reaction rate was studied by unsteady calculation for modal premixed combustor, and the unsteady heat release occurred at the top of the flame. The de- lay times of 0.6, 0.3, 0.9, 0.6ms were obtained for equivalence ratios of 0. 72, 0.8, 0.88 and 0.97 respectively in four cases based on the phase difference of pressure and temperature signals. The linear stability analysis obtained the real part and imaginary part of frequency of longitudinal mode for modal premixed combustor, and the negative imaginary part represen- ted linear instability. The results show that the second, third, and fourth longitudinal modes are linear instability in the first five longitudinal modes. The imaginary part of the third lon- gitudinal mode has the largest absolute value, indicating the largest growth rate in small dis- turbance. So there is the biggest possibility to occur linear unstable and combustion instabili- ty for the third longitudinal mode in disturbance.