Intrinsic Thermoacoustic Instability of Premixed Flames
Intrinsic Thermoacoustic Instability of Premixed Flames
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DOI：
10.1016/j.combustflame.2014.06.008
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发表时间：
2015
影响因子：
4.4
通讯作者：
T. Emmert;S. Bomberg;W. Polifke
中科院分区：
文献类型：
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作者：
T. Emmert;S. Bomberg;W. Polifke
研究了速度敏感预混火焰的热声稳定性。一个因果关系表示的流量火焰声相互作用揭示了火焰的内在反馈机制。反馈回路可以描述如下：上游速度扰动引起热释放速率的调制，这又产生在上游方向上行进的声波，其中声波影响声速并且因此闭合反馈回路。这种反馈动力学的共振，这被确定为固有的本征模式的火焰，具有重要的后果的动力学和稳定性的燃烧过程中，一般和特别是火焰。研究发现，由于火焰内部反馈机制，火焰-声相互作用对声功率的放大在接近本征值的频率处可以达到很高的水平。这是严格显示通过评估的“不稳定的潜力”，从平衡的声能通量跨越火焰。人们获得最大（以及最小）功率放大的因素。基于声能放大原理，引入小增益定理作为燃烧系统稳定性判据。它允许制定燃烧器或火焰的声学特性的优化标准，而不考虑由燃烧室或增压室提供的边界条件。首先用简单的n-τ模型和代表湍流旋流燃烧器的火焰传递函数来举例说明这些概念和方法。
The thermoacoustic stability of velocity sensitive premixed flames is investigated. A causal representation of the flow-flame-acoustic interactions reveals a flame-intrinsic feedback mechanism. The feedback loop may be described as follows: An upstream velocity disturbance induces a modulation of the heat release rate, which in turn generates an acoustic wave traveling in the upstream direction, where it influences the acoustic velocity and thus closes the feedback loop. The resonances of this feedback dynamics, which are identified as intrinsic eigenmodes of the flame, have important consequences for the dynamics and stability of the combustion process in general and the flame in particular. It is found that the amplification of acoustic power by flame-acoustic interactions can reach very high levels at frequencies close to the intrinsic eigenvalues due to the flame-internal feedback mechanism. This is shown rigorously by evaluating the “instability potentiality” from a balance of acoustic energy fluxes across the flame. One obtains factors of maximum (as well as minimum) power amplification. Based on the acoustic energy amplification, the small gain theorem is introduced as a stability criterion for the combustion system. It allows to formulate an optimization criterion for the acoustic characteristics of burners or flames without regard of the boundary conditions offered by combustor or plenum. The concepts and methods are exemplified first with a simplistic n-τ model and then with a flame transfer function that is representative of turbulent swirl burners.