声激励下旋流钝体火焰的非线性响应实验

Experiment on nonlinear response of swirling bluff-body flame with external acoustic forcing

在常压条件下对二甲醚贫燃预混旋流钝体火焰施加100 Hz的外加声激励,运用高速OH*化学发光成像和粒子图像测速锁相同步测量的实验方法,针对不同速度脉动比例下的火焰形态特征和流场特征的动态变化开展可视化测量,得到火焰描述函数。研究发现,随着声波幅值增大,火焰的热释放率将先线性增加,在到达扰动临界点后,火焰出现非线性响应现象,实验中的临界速度脉动比例为16%。同时,通过逆阿贝尔变换和本征正交分解等方法比较了火焰线性响应与非线性响应工况的流场和燃烧场差异,发现在非线性响应工况下火焰形态的涡卷起和流场中的外回流区涡脱落特征增强,这表明外回流区涡脱落增强现象可能是诱发火焰非线性响应的原因。

The experimental measurement of lean premixed swirling bluff-body dimethyl ether flames excited by an external acoustic forcing at 100 Hz was carried out at atmospheric pressure.With the help of the phase-locked high-speed OH*chemiluminescence imaging and particle image velocimetry,the visualization of the flame dynamic characteristic of both the flame shape and the flame flow field with different pulsation amplitudes of the velocity was achieved.Based on these images,the dynamic process of the flame was analyzed by the flame describing function.It was found that the heat release rate first linearly increased as the forcing amplitudes increased,and the nonlinear flame response was recognized when the critical value of the velocity fluctuation ratio was reached.The velocity fluctuation ratio of 16%was the critical value in this experiment.Meanwhile,the difference between linear and nonlinear flame responses was analyzed by means of inverse Abel transformation and proper orthogonal decomposition.The experimental results showed that the vortex roll-up of the flame shape and the vortex shedding of the flame flow field was enhanced in the nonlinear flame response.From the above analysis,it can be inferred that the enhancement of vortex shedding in the outer recirculation zone of the flame flow field induced the nonlinear flame response.