In this study, experimental measurements are performed on a swirl-stabilized combustor to study the nonlinear combustor dynamic characteristics under acoustic excitations. The imposed acoustic disturbances with different frequencies and amplitudes generated by a loudspeaker are applied to the combustion system. The acoustic pressure oscillations and heat release rate fluctuations are measured using acoustic pressure transducers and a photomultiplier tube equipped with a bandpass OH^* filter, respectively. Various parametric studies are conducted to evaluate the effects of the equivalent ratio \(\phi\), amplitude A_f, and frequency f_f of the acoustic excitations on the combustor dynamics. The obtained results indicate that the combustor experiences frequency locking-in phenomenon accompanied by high amplitude acoustic oscillations when f_f is close to the natural frequency f_a of the combustor quarter-wave mode. Such physical phenomena are observed even for a low forcing wave amplitude. However, heat release rate fluctuations reach saturation at high amplitude excitations. Moreover, the combustor experiences super-harmonic resonances when f_f is close to f_a/2 or f_a/3. Under such conditions, high amplitude excitations are required to stimulate the natural resonant mode, while the heat release rate fluctuations rarely reach saturation. Cross-correlation and cross-power spectral density analyses on the OH^* chemiluminescence and acoustic pressure signals reveal that super-harmonic resonances are caused by “quasi-couplings” between the acoustic pressure and unsteady heat release. Further, the results demonstrate that the excited natural mode oscillations affect the acoustic wave characteristics at the inlet section, while they hardly influence the heat release rate fluctuations. The obtained results indicate that the equivalence ratio has a negligible effect on the combustor dynamics under forced conditions. Finally, discussions are provided to address the influences of the excited natural mode oscillations on the experimental measurements of the flame describing function (FDF). The achieved acoustic velocity disturbances at the injector outlet are suppressed by excited natural mode oscillations, which confine the velocity disturbance amplitude within a narrow range when f_f matches f_a. Hence, excited natural mode oscillations should be avoided in practice if we need to measure the FDF under a wide range of acoustic velocity amplitudes. The nonlinear characteristics of forced oscillations studied in this paper are crucial to the development of control strategy and FDF measurement.

在这项研究中，在涡旋稳定燃烧器上进行了实验测量，以研究声激发下非线性燃烧器的动态特性。由扬声器产生的具有不同频率和幅度的强加的声干扰被施加到燃烧系统。分别使用声压传感器和配备有带通OH ^*滤波器的光电倍增管来测量声压振荡和放热率波动。进行了各种参数研究，以评估等效比\（\ phi \），幅度A _f和频率f _f的影响声激励对燃烧室动力学的影响。获得的结果表明，当f _f接近燃烧器四分之一波模式的固有频率f _a时，燃烧器会出现频率锁定现象，并伴有高振幅的声音振荡。即使在低强迫波振幅下也观察到这种物理现象。然而，在高振幅激励下，放热速率的波动达到饱和。此外，当f _f接近f _a / 2或f _a时，燃烧室会经历超谐共振。/ 3。在这种情况下，需要高振幅激励来激发自然共振模式，而放热速率的波动很少达到饱和。OH上的互相关和互功率谱密度分析^*化学发光和声压信号表明，超谐共振是由声压和不稳定的热释放之间的“准耦合”引起的。此外，结果表明，激发的自然模式振荡会影响入口部分的声波特性，而几乎不会影响放热速率的波动。获得的结果表明，当量比对强制条件下的燃烧室动力学影响微不足道。最后，提供了讨论以解决激发自然模式振荡对火焰描述函数（FDF）的实验测量的影响。激发的自然模式振荡可抑制喷油器出口处实现的声速扰动，f _f匹配f _a。因此，如果需要在较宽的声速幅度范围内测量FDF，则应在实践中避免激发自然模式振荡。本文研究的强迫振荡的非线性特性对于控制策略和FDF测量的发展至关重要。