Abstract: In order to use the correct flashback control methods，flashback type should be distinguished in advance. In the present investigation，the effects of mixing zone structure on flashback limit and flashback type were investigated with CFD simulation over a wide range of mixing length(L)and characteristic hydraulic diameter of mixing zone exit(D). Moreover，numerical experiments were arranged by Design of Experiments (DOE) method and results were dealt with analysis of variance. Based on the simulation results and the analysis，three conclusions can be drawn. Firstly，both L and D have prominent effects on flashback limit. Furthermore，either boundary flashback or combustion induced vortex breakdown(CIVB) flashback could be prevented by decreasing the residence time of mixture inside the mixing zone. Secondly，two critical dimensionless limits (L/D)cri are found to distinguish flashback type. If L/D≤(L/D)cri1，boundary layer flashback occurs. If L/D>(L/D)cri2，CIVB flashback occurs，otherwise maybe only CIVB flashback or both CIVB and boundary layer flashback occur. Finally，the critical azimuthal vorticity for CIVB flashback is changed by L/D. With the increase of L/D，critical azimuthal vorticity decreases which makes CIVB flashback more prone to be initiated.

Key words: Combustion induced vortex breakdown(CIVB)flashback；Boundary layer flashback；Flashback type；Azimuthal vorticity；Hydrogen flame

摘要： 为了区分不同类型的回火形式，以便可以对不同类型的回火施加不同的控制方法，引入试验设计(DOE)方法和方差分析方法数值分析了预混段长度L和预混段出口处水力直径D对回火形式和回火极限的影响。主要得到如下结论:L和D对回火极限均有显著影响，通过减少混合物在预混段内的停留时间可以同时改善燃烧诱导涡破碎(CIVB)回火和边界层回火；L/D存在两个临界值，当L/D≤(L/D)cri1时发生边界层回火，当L/D>(L/D)cri2时发生CIVB回火，当(L/D)cri1

关键词: 燃烧诱导涡破碎回火；边界层回火；回火形式；切向涡量；氢燃料火焰