旋进涡核与火焰面耦合作用对燃烧稳定性影响的数值研究

Numerical Study on the Influence of Precessing Vortex Core Coupling with Flame Surface on Combustion Stability

对PRECCINSTA模型燃烧室中的动态燃烧过程进行了大涡模拟数值研究。在固定当量比为0.7时,对热功率分别为10、35kW的两种燃烧工况的燃烧特性进行了非定常数值模拟,模拟结果与实验数据吻合良好。研究表明,两种工况的冷态流场均在射流与内回流区之间的内剪切层中存在一个螺旋形的旋进涡核(PVC),而热态时却展现出了不同的流场特性和火焰形式。当热功率为10kW时,火焰呈现V型且燃烧稳定,流场内剪切层中的PVC消失,仅存在对称布置的旋涡;当热功率为35kW时,火焰呈现M型且发生了热声耦合不稳定燃烧现象,此时流场内剪切层中的PVC依然存在。通过对不稳定工况下瞬态流场、温度场及放热特性的分析,发现PVC引起了规律性的火焰卷曲,对低温未燃和高温已燃气体的混合起到了加速作用,从而导致了局部区域内混合物的引燃。这些过程与PVC引起的周期性的涡运动直接相关,可以证实PVC对燃烧及放热的影响是35kW工况下发生不稳定燃烧的重要因素。

Large eddy simulation（LES）was used to investigate the combustion dynamics on a lab scaled combustion chamber,which is well known as PRECCINSTA combustor.Transient threedimensional numerical simulations at the two different thermal powers（10 kW and 35 kW）with a fixed equivalence ratio of 0.7 were carried out.The predicted results were compared with the experimental data and good agreements were showed.A precessing vortex core（PVC）in the inner shear layer（ISL）,which existed between the swirling jet and the inner recirculate zone（IRZ）,could be seen in the cold flow field of both conditions.However,two different flow and combustion dynamics appeared when combustion occurred.At thermal power of 10 kW,there was a V-shaped flame with stable combustion,PVC disappeared,and the vortices arrangement was symmetrical in the ISL.However,there was a M-shaped flame with a PVC in the ISL and thermoacoustic coupling combustion instability occurred at thermal power of 35 kW.Through the analysis of the characteristics of the flow,temperature and heat release field,it is found that the flame surface was wrinkled periodically by the PVC,which enhanced the mixture of cold freshgas and hot burned gas,and then the mixture was ignited in a local area.These effects were directly related to the periodic vortex motion induced by PVC.It is confirmed that the influence of PVC on flame surface and heat release is an important factor triggering the combustion instability at thermal power of 35 kW.