火焰面波动诱发漩涡脱落的热声耦合机理研究与理论建模

The ultra-low NOx emission combustors (in gas turbine) with lean premixed combustion technology are susceptible to combustion instability. However, the methods to predict and suppress combustion instability are still not mature enough because of the complexity of the mechanism. The objective of the study is to improve the existing mechanism of combustion instability and build a new model of dynamic heat release rate by means of the theory of vortex shedding induced by flame surface variation and the method of acoustic modal analysis, which will provide a theoretical basis for the forecasting methods and suppression strategies of thermo-acoustic oscillations in engineering applications. Firstly, the research scheme sum up the advantages of acoustic-flame interaction mechanism and vortex shedding mechanism, and present the thermo-acoustic theory of vortex shedding induced by flame surface wave and establish the corresponding dynamic model of heat release rate in an ideal combustor. Secondly, the acoustic modal analysis method is used to solve natural frequency and vibration mode of the combustor with dynamic heat release, and the effect of combustor geometry, operating parameters and fuel components to thermo-acoustic oscillation phenomenon is researched. Finally, through comparing experimental results with the results of modal analysis, modify the dynamic heat release rate model, and improve the mechanism of thermo-acoustic oscillation, so as to accurately predict thermo-acoustic oscillation in combustor design phase or inhibit this phenomenon in operational stage.

基于稀态预混燃烧技术的新型超低NOx燃烧室（燃气轮机）极易遭到热声振荡的困扰，然而由于其发生机理的复杂性，人们却依然不能有效地预测和抑制热声振荡问题。本课题研究目标是基于火焰面波动诱发漩涡脱落理论和燃烧室声场模态分析方法，完善现有热声振荡机理、构建新型动态热释放率模型，为面向工程应用的热声振荡预测方法和抑制策略提供理论基础。研究方案首先借鉴声-火焰面波动机理和漩涡脱落机理的优势（规避其缺陷），以理想燃烧室为研究对象，提出火焰面波动诱发漩涡脱落的热声耦合机理，并建立相应动态热释放率模型；其次利用声场模态分析方法求解燃烧室存在动态热释放时的固有频率和模态振型，探索燃烧室几何结构、运行参数和燃料成分等对热声振荡现象的影响（规律）；再次通过实验结果与模态分析结果的对比，修正燃烧动态热释放率模型，从而完善热声振荡机理。

稀态预混燃烧技术最具低污染排放优势，最近二十年在燃气轮机领域得到广泛的应用，然而该技术的发展却受到热声振荡问题的阻碍。国内外学者在热声振荡的研究中取得了很多有价值的成果，但是由于热声振荡的机理的复杂性，现在依然不能有效地预测和抑制热声振荡问题。本项目对燃气轮机热声振荡问题通过理论推导、数值模拟和实验验证相结合的方法进行了深入的研究。首先，在理论推导方面发展了声-火焰面作用机理的动态热释放率模型，分析了影响燃烧热释放率波动的主要因素，燃烧热膨胀效应对动态热释放率传递函数的幅频特性具有较大影响，火焰传播速度是动态热释放率模型的关键参数，能够强烈地影响声压与热释放率之间的时间延迟。其次，在数值模拟方面验证了基于动态热释放率模型的声场模态分析方法对热声振荡研究的有效性，通过频域分析获得了模型燃烧室声场的固有频率、声压振型和振幅增长率随温度和当量比的变化规律，通过时域分析获得了模型燃烧室热声振荡稳定区间和非稳定区间。最后，在实验研究方面分析了动态热释放率与声压作用规律，确认了漩涡脱落是热声振荡的发生机理，但未能证明火焰面波动是激发漩涡脱落的直接原因，发现声压振荡从非热致发声、低频热致发声、高频热致发声至热声振荡的变化规律，热声振荡现象是高频热致发声的极端情况，是由于热致发声的频率与燃烧室固有频率接近，导致的共振现象。