旋流强度对甲烷/空气预混火焰CIVB回火的影响

Effects of Swirl Strength on Combustion Induced Vortex Breakdown (CIVB) Flashback in Methane/Air Premixed Flames

关键词:  燃烧诱导涡破碎回火  旋流数  切向涡量  流动不稳定  旋流强度

Key words:  Combustion induced vortex breakdown flashback  Swirl number  Azimuthal vorticity  Flow instability  Swirl strength

摘要:

为了研究旋流强度对甲烷/空气预混火焰燃烧诱导涡破碎(CIVB)回火的影响，以便深入理解CIVB回火的机理进而抑制回火，采用二维轴对称模型，并使用用户自定义函数(UDF)修改动量守恒方程来模拟旋流，得到了甲烷/空气预混火焰在不同旋流数下的CIVB回火极限，通过负切向涡量和流动不稳定理论分析了回火过程中的涡破碎。结果表明，对于无中心体旋流预混喷嘴中甲烷/空气火焰的CIVB回火，旋流数从0.409增加到0.416，先促进回火后抑制回火；对于同一个喷嘴结构，不同旋流数下发生CIVB回火时流场满足相同的涡破碎条件，即负切向涡量最大值约为5.5×104s-1，从宏观尺度分析其实质是流动不稳定扰动因子相同。

Abstract:

In order to deepen understanding the flashback due to combustion induced vortex breakdown (CIVB) and prevent it，the effects of swirl strength on CIVB flashback in methane/air premixed flames were investigated. Flashback limits of methane/air premixed flames at different swirl numbers were obtained by numerical simulation with two-dimensional axisymmetric model and implementing user defined function(UDF)to simulate swirl by modifying the momentum conservation equations. Vortex breakdown during flashback was analyzed by the negative azimuthal vorticity and the flow instability theory. For methane/air flames in the swirl-premixed nozzle without a centerbody，increase of swirl number from 0.409 to 0.415 firstly enhances CIVB flashback and then prevents it. For one nozzle structure，critical CIVB flashback at different swirl numbers meets the same condition of vortex breakdown，which means the maximum values of negative azimuthal vorticity are about 5.5×104s-1，and its essence is that the disturbance factors of flow instability are the same from a macro scale analysis.