The combined dynamics of swirler and turbulent premixed swirling flames
The combined dynamics of swirler and turbulent premixed swirling flames
复制标题
DOI：
10.1016/j.combustflame.2010.02.011
复制
发表时间：
2010-09
影响因子：
4.4
通讯作者：
P. Palies;D. Durox;T. Schuller;S. Candel
中科院分区：
文献类型：
--
作者：
P. Palies;D. Durox;T. Schuller;S. Candel
通过对入射速度扰动的响应，研究了预混密闭旋流火焰的动力学特性。指定为火焰描述函数（FDF）的广义传递函数是通过扫描从0到400Hz的频率范围并通过改变总体速度的0%到72%之间的均方根波动水平来确定的。不稳定放热速率由OH*自由基的发射强度推导而来。这一全局信息由相位条件阿贝尔变换发射图像补充。这种处理产生光发射的分布。通过假设光强与热释放率成正比，可以推导出Wm−3中不稳定热释放率的分布，并可以看到在调制周期和不同强迫频率下它是如何随时间演变的。这些数据可用于确定不稳定状态，但也为控制旋转火焰动力学的机制提供线索。从实验和分析中发现，涡旋器受到来自上游流形的轴向声波的作用，在其下游产生涡度波。然后，火焰受到以声速传播的轴向声扰动和以流速转换的方位角速度扰动。最终的结果是，动力响应和非定常热释放率是由这些轴向和诱导的方位角速度扰动的综合作用决定的。前者的扰动引起喷油器唇部涡的脱落，使火焰末端卷起；后者的扰动有效地扰动了旋流数，使火焰根部发生角振荡。这种运动相当于燃烧速度的扰动所引起的运动。入射扰动之间的相位由旋流器和喷射器之间的对流时间延迟控制。不同扰动之间的相摄或相消干涉显示出在某些频率下所观察到的低增益和高增益。
The dynamics of premixed confined swirling flames is investigated by examining their response to incident velocity perturbations. A generalized transfer function designated as the flame describing function (FDF) is determined by sweeping a frequency range extending from 0 to 400Hz and by changing the root mean square fluctuation level between 0% and 72% of the bulk velocity. The unsteady heat release rate is deduced from the emission intensity of OH*radicals. This global information is complemented by phase conditioned Abel transformed emission images. This processing yields the distribution of light emission. By assuming that the light intensity is proportional to the heat release rate, it is possible to deduce the distribution of unsteady heat release rate in Wm−3and see how it evolves with time during the modulation cycle and for different forcing frequencies. These data can be useful for the determination of regimes of instability but also give clues on the mechanisms which control the swirling flame dynamics. It is found from experiments and demonstrated analytically that a swirler submitted to axial acoustic waves originating from the upstream manifold generates a vorticity wave on its downstream side. The flame is then submitted to a transmitted axial acoustic perturbation which propagates at the speed of sound and to an azimuthal velocity perturbation which is convected at the flow velocity. The net result is that the dynamical response and unsteady heat release rate are determined by the combined effects of these axial and induced azimuthal velocity perturbations. The former disturbance induces a shedding of vortices from the injector lip which roll-up the flame extremity while the latter effectively perturbs the swirl number which results in an angular oscillation of the flame root. This motion is equivalent to that which would be induced by perturbations of the burning velocity. The phase between incident perturbations is controlled by the convective time delay between the swirler and the injector. The constructive or destructive interference between the different perturbations is shown to yield the low and high gains observed for certain frequencies.