基于CH自由基发光的旋流火焰放热率时空特性研究

Study of the temporal and spatial characteristics for swirling flame heat release rate based on CH chemiluminescence

对不同工况下CH_4/air旋流火焰的放热率在时间上的热声振荡现象和空间的三维形态转变两方面进行了研究。在燃烧形态转变方面,由于旋流火焰的复杂流场分布特性,采用基于化学自发光的三维计算层析技术(3D-CTC),测量了雷诺数从5 000到20 000的三个工况下旋流燃烧的CH*发光三维火焰结构。以此表征放热率的三维分布,实现对旋流火焰放热空间形态的测量。该诊断方法通过对旋流火焰发光在8个视角下的二维成像,结合层析重建算法得到其三维CH*分布信息。为验证重建保真度,将重建后结果二维可视化与高速摄影下的二维时均结果进行对比,结果表明重建误差在5%以内。研究中,分析了不同雷诺数下放热率的空间变化规律,结果显示所有实验工况下放热率的垂直于喷嘴方向的变化程度比沿喷嘴轴向的要剧烈;而随着雷诺数增加,最大的放热区表现出了明显的向后推进趋势。在旋流燃烧的热声振荡方面,利用CH*的二维高速摄影,对旋流燃烧的放热率不稳定性进行研究,发现放热率的振荡频率随着雷诺数的增大逐渐增加。

Several swirling CH4/air diffusion flames were investigated in a gas turbine model combustor via the temporal phenomenon of thermos-acoustic and the spatial flame mode transition.In the combustion mode transition,three-dimensional computed tomography of chemiluminescence(3 D-CTC)technique was utilized due to the complexity of swirling combustion flow field.The 3 Demissions of CH*were measured and taken as qualitative indicators of the heat release rate under three Reynolds number conditions(from 5000 to 20 000).This 3 D measurement method utilized 8 multi-directional CH*images as inputs combined with tomographic algorithms to compute the 3 Ddistribution of CH*intensities.In order to verify the reconstruction fidelity,the two-dimensional visualization of the reconstructed shape was compared with the time-averaged projection under high-speed photography,and the results showed that the reconstruction error was within 5%.In this study,the transitions of heat release area with Reynolds number were analyzed,and the results showed that the heat release rate changed more obviously along the nozzle radical direction than the axis direction,and the largest heat release area moved forward significantly.The thermoacoustic study was obtained by high speed CH*images,finding that the oscillating frequency of heat release increased with the increase of the Reynolds number.