采用贫预混燃烧方式容易发生燃烧振荡现象，这是当前发展干式低污染燃气轮机燃烧室难以回避的问题之一。燃烧振荡过程中会形成剧烈的压力脉动和火焰不稳定现象，严重危害燃气轮机的安全稳定运行。这种振荡现象是热声耦合导致的燃烧系统固有的不稳定性，也称为热声不稳定。本文针对实验中发现的一类特殊的热声不稳定现象——拍振，开展实验研究与理论分析，并对燃烧系统中的拍振进行主动控制研究，分析其与极限环振荡的主动控制的区别。 本文研究的燃烧系统包括：1）黎开管燃烧器（层流）；2）旋流预混燃烧室（湍流）。前者结构较简单，便于系统地开展实验研究与理论分析，其研究结果可以进一步通过后者的实验研究进行验证，后者更接近于工业燃烧室。黎开管燃烧器中的实验研究发现，拍振一般发生在热声耦合不稳定的临界工况附近，拍振的幅值调制频率一般在1 Hz 量级。通过拍振条件下的火焰动力学分析，认为低频的火焰脉动过程是导致拍振的幅值调制现象的主要原因，而这种低频火焰脉动与层流火焰固有的扩散-热不稳定性有关。考虑不同时间尺度上的火焰动力学特性，本文建立了能够预测拍振的热声耦合模型，利用此模型可以对拍振现象的发生规律与时变特性进行预测与分析。通过黎开管燃烧器主动控制的数值仿真与实验研究，比较了移相控制、相位补偿控制、比例积分微分控制（PID）和自校正调节控制（STR）四种控制算法的控制效果。旋流预混燃烧室中的实验研究表明，湍流条件下的拍振现象其基本特征与层流燃烧器中类似，但是其拍振特征随工况条件的变化较明显。针对旋流预混燃烧室中的主动控制，本文提出了一种通过实验测量建立热声耦合系统的非线性模型的方法，并通过实验测量与数值仿真进行了验证。最后，采用电动气流扬声器作为执行机构，对旋流预混燃烧室中燃烧振荡的主动控制进行了实验研究。 本文针对热声耦合拍振现象的研究，拓展了对于热声不稳定现象中非线性特性的认识，对于深入理解燃烧系统中存在的复杂热声耦合振荡现象具有重要意义。由于拍振现象通常发生在热声不稳定的临界工况附近，对这类振荡现象的研究也有助于燃烧振荡的预警与控制。通过对拍振的主动控制的研究，能够检验控制算法的长期稳定性，为提高实际燃烧系统中主动控制的可靠性提供参考。
Lean premixed combustion technique is prone to combustion oscillations. This is one of the unavoidable problems in development of dry low pollution gas turbine combustor. Combustion oscillations give rise to intense pressure oscillations and flame pulsations, which seriously harm the safe and stable operation of gas turbines. These oscillations are caused by thermoacoustic coupling and inherent to combustion systems They are also known as thermoacoustic instabilities. A special type of thermoacoustic instabilities named beating oscillations are focused in this thesis, and they are investigated experimentally and theoretically. The active control of beating oscillations in combustion systems is also investigated with comparison to the active control of limit cycle oscillations. Two combustion systems are considered in this study: 1) a Rijke tube burner (laminar); 2) a premixed swirl combustor (turbulent). The former has a simple structure, in which it is convenient to conduct experimental research and theoretical analysis systematically. The results in the former combustion system can be verified by experimental study in the latter one, which is more close to the industrial combustors. Experimental study in the Rijke tube burner found that beating oscillation usually occurs in the vicinity of the critical conditions for thermoacoustic instability. The amplitude modulation frequency is in the order of 1 Hz. By analysis of the flame dynamics during beating oscillations, it is suggested that the low-frequency flame pulsation is the main reason to the amplitude modulation behavior in beating oscillations. This low frequency flame pulsation can be due to the di usive-thermal instability which is inherent to laminar flames. Considering the flame dynamics at di erent time scales, a thermoacoustic coupling modelis established for simulation of beating oscillations. It is able to predict the occurrenceconditions of beating oscillations and can be used to analyse the time-varying characteristics of beating oscillations. In the numerical simulation and experimental study on active control of the Rijke tube burner, the control e ectiveness of four types of control algorithms are compared: the phase shift controller, phase compensation controller, PIDcontroller and self-tuning controller (STR). Experimental study results in the premixed swirl combustor show that the basic characteristics of beating oscillations under turbulent flow conditions are similar to the ones in laminar burners, but the time-varying characteristics are more sensitive to the variation of working conditions. As to the active control in the premixed swirl combustor, this thesis develops a method to establish the nonlinear model of the thermoacoustic system by experimental measurement, and it has been verified by experimental measurement and numerical simulation. Finally, experimental studies on the active control of combustion oscillations in the premixed swirl combustor are conducted by using an electropneumatic loudspeaker as the actuator. This thesis investigates the thermoacoustic beating oscillations and shows the influence of multiscale flame dynamics on the time-varying charicteristics of thermoacoustic instabilities. It expands the understanding of the nonlinear characteristics of thermoacoustic instability, and it has great significance for in-depth understanding of complexthermoacoustic oscillations in combustion systems. Because the beating oscillations usually occur near the critical conditions of thermoacoustic instabilities, the research on this kind of oscillations is helpful to the early warning and control of thermoacoustic instabilities. Through the active control of the beating oscillations, the long-term stability of a control algorithm can be tested, which can provide reference for improving the reliability of active control in practical combustion systems.
