旋流强度对氢气预混火焰CIVB回火的影响 *

Effects of Swirl Strength on CIVB Flashback in Hydrogen Premixed Flames

关键词:  燃烧诱导涡破碎回火  旋流数  氢气预混火焰  负切向涡量  湍流火焰速度

Key words:  Combustion induced vortex breakdown flashback  Swirl number  Hydrogen premixed flames  Negative azimuthal vorticity  Turbulent flame speed

摘要:

为了研究旋流强度对氢气预混火焰燃烧诱导涡破碎(CIVB)回火的影响，以便深入理解氢气的CIVB回火特点进而减弱回火，首先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，得到了不同旋流数下氢气预混火焰的CIVB回火极限，然后从旋流强度对流场特性和火焰特性两方面的影响进行深入分析。结果表明:对于无中心体旋流预混喷嘴中氢气火焰的CIVB回火，旋流数从0.409增加到0.432，从流场条件分析，旋流数增加使负切向涡量增加，对回火起促进作用；从火焰条件分析，旋流数增加使氢气湍流火焰速度先增加后减小，最后趋于猝熄，对回火先起促进作用后起抑制作用。流场和火焰条件共同决定了旋流数对氢气预混火焰CIVB回火的影响趋势，即旋流数增加先促进回火后抑制回火。

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 hydrogen premixed flames were investigated. Flashback limits of hydrogen premixed flames 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. Effects of swirl strength on flow aerodynamic characteristics and flame characteristics were analyzed in detail. The results are as follows: for hydrogen flames in the swirl-premixed nozzle without a centerbody， increase of swirl number from 0.409 to 0.432 enhances flashback due to the increase of negative azimuthal vorticity from the aspect of the flow conditions. From the aspect of the flame conditions， increase in swirl strength firstly enhances flashback and then prevents it， because the turbulent flame speed of hydrogen flame firstly increases with increasing swirl strength and then decreases， finally toward quenching. Both aspects together determine the effects of swirl strength on CIVB flashback in hydrogen premixed flames. That is， flashback is firstly enhanced and then prevented with increasing swirl strength.