Control of combustion driven acoustic oscillations using plasma discharges

燃烧不稳定性是现代航空发动机和固定式燃气轮机燃烧室设计的主要问题。一个有前途的方法来抑制高振幅的压力脉动与这些热声不稳定性是基于系统动力学的主动控制。在过去的20年里，一些研究已经证明了这种方法的能力，主要使用声学强迫和燃料喷射调制作为驱动机制。然而，这些方法在全尺寸发动机中的适用性仍然有限，由于可用的致动器技术和性能的限制。2012年，参与拟议项目的两个合作伙伴，EM 2C（法国）和TUB（德国），成功地测试了使用非平衡等离子体放电来控制燃烧动态。概念验证已经实现，纳秒重复脉冲（NRP）放电可以用作主动控制燃烧不稳定性的致动机构，而没有传统致动器（例如扬声器或燃料阀）的缺点。然而，虽然这项初步研究是有希望的，等离子体和火焰动力学之间的非稳态耦合仍然不清楚，必须进一步研究，以揭示这种新方法的全部潜力。因此，拟议的项目旨在（1）获得燃烧动力学和非平衡等离子体放电耦合的基本理解，（2）非平衡等离子体放电主动控制燃烧不稳定性潜力的实验评价。试验工作将在法国和德国进行，以便利用这两个伙伴的互补专长。等离子体声学和等离子体火焰相互作用的基础研究将在专门的通用设置进行。通过对等离子体-火焰相互作用的数值模拟，建立了NRP等离子体放电对贫油预混火焰燃烧动力学影响的经验模型。本文将研究NRP放电对旋流稳定贫油预混火焰动力学的影响，包括声学、化学和流体动力学效应。等离子体激励器将在一个具有完全湍流旋流稳定火焰的大气燃烧室试验台上实现。火焰对等离子体强迫的响应将用声学和光学方法测量，并且所获得的致动器传递函数将与热声系统模型结合使用以开发适当的控制方案。反馈控制，然后将被施加到减轻燃烧不稳定性的试验台。

Combustion instabilities are a major issue for the design of modern combustion chambers in aero-engines and stationary gas turbines for power generation. One promising approach to suppress the high-amplitude pressure pulsations associated with these thermoacoustic instabilities is based on active control of the system dynamics. Several studies over the past 20 years have demonstrated the capability of this approach, using mostly acoustic forcing and fuel injection modulation as actuation mechanisms. However, the applicability of these methods in full-scale engines remains limited, due to restrictions in available actuator technology and performance.In 2012, the two partners involved in the proposed project, EM2C (France) and TUB (Germany), successfully tested the use of non-equilibrium plasma discharges to control combustion dynamics. The proof of concept has been realized that nanosecond repetitively pulsed (NRP) discharges can be used as an actuation mechanism for active control of combustion instabilities, without the drawbacks of traditional actuators such as loudspeakers or fuel valves. However, while this preliminary study was promising, the unsteady coupling between plasma and flame dynamics remains unclear and must be further investigated to uncover the full potential of this novel approach.The proposed project therefore aims at (1) acquiring a fundamental understanding of the coupling of combustion dynamics and non-equilibrium plasma discharges, (2) the experimental evaluation of the potential of non-equilibrium plasma discharges for active control of combustion instabilities. Experimental work will be performed in France and in Germany, in order to benefit from the complementary expertise of the two partners. Fundamental studies of plasma-acoustic and plasma-flame interaction will be carried out, in dedicated generic set-ups. With the help of numerical simulations of plasma-flame interaction, an empirical model of the effect of NRP plasma discharges on the combustion dynamics of lean premixed flames will be derived. The influence of NRP discharges on the dynamics of swirl-stabilized lean premixed flames will be investigated, including acoustic, chemical and hydrodynamic effects. A plasma actuator will be implemented in an atmospheric combustor test-rig with a fully turbulent swirl-stabilized flame. The response of the flame to plasma forcing will be measured with acoustic and optical methods, and the obtained actuator transfer function will be used in conjunction with a thermoacoustic system model to develop appropriate control schemes. Feedback control will then be applied to mitigate combustion instabilities in the test-rig.