Nonlinear analysis of an acoustically excited laminar premixed flame
Nonlinear analysis of an acoustically excited laminar premixed flame
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DOI：
10.1016/j.combustflame.2015.09.035
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发表时间：
2016
影响因子：
4.4
通讯作者：
S. Schlimpert;M. Meinke;W. Schröder
中科院分区：
文献类型：
--
作者：
S. Schlimpert;M. Meinke;W. Schröder
通过数值求解可压缩流体的守恒方程，研究了由流入速度分布的幅度变化定义的扰动场与包含气体膨胀效应的层流预混火焰之间的完全耦合双向相互作用的非线性效应。两个燃烧与未燃烧温度比的火焰前缘扰动的高次谐波结果显示了火焰响应的非线性传递如何受到流体动力学不稳定性和剪切层效应的影响。对于低马克斯坦长度值下所研究的温度比，可以通过降阶模型（ROM）很好地预测基本强迫频率下的火焰响应，即火焰描述函数，其中火焰拉伸效应和流体动力学不稳定性之间的平衡是微不足道的。然而，在高马克斯坦长度下，火焰拉伸和流体动力学不稳定性之间的平衡会影响所有激发幅度下的火焰响应特性。火焰锋扰动的非线性研究表明，详细计算和 ROM 预测之间整体非线性火焰响应的高次谐波含量的差异位于火焰袋分离之前的火焰锋处。因此，剪切层和流体动力不稳定效应通过在火焰底部引入的非线性、火焰袋分离的位置以及火焰尖端的湮灭过程（特别是在高马克斯坦长度值时）决定了火焰响应的非线性特征。此外，还将火焰底座运动响应与最近开发的降阶火焰底座模型进行比较，以了解有关燃烧器唇部火焰附着假设的发现。
The nonlinear effects of the fully coupled two-way interactions between a disturbance field defined by an amplitude variation of the inflow velocity distribution and a laminar premixed flame incorporating gas expansion effects are investigated by numerically solving the conservation equations of a compressible fluid. Results of the higher harmonics of the flame front perturbation for two burnt to unburnt temperature ratios show how the nonlinear transfer of flame response is affected by the hydrodynamic instability and the shear layer effect. The flame response at the fundamental forcing frequency, i.e., the flame-describing function can be well predicted by the reduced-order model (ROM) for both investigated temperature ratios at low Markstein length values, where the balance between the flame stretch effects and the hydrodynamic instability is insignificant. However, at high Markstein lengths the balance between the flame stretch and the hydrodynamic instability influences the flame response characteristics at all excitation amplitudes. The nonlinear study of the flame front perturbation indicates that differences in the higher harmonic content of the overall nonlinear flame response between the detailed computation and the ROM predictions are located at the flame front just before the flame pockets separate. Thus, the shear layer and the hydrodynamic instability effect determine the nonlinear character of the flame response through the nonlinearity introduced at the flame base, the location of flame pocket separation, and the annihilation process at the flame tip especially at high Markstein length values. In addition, the flame base movement response is compared to a recent developed reduced-order flame base model to understand the findings with respect to the assumption of flame attachment at the burner lips.