Flame-head splitting and local compression under half-open confinement during premixed hydrogen–air propagation

Premixed hydrogen–air deflagration in a half-open channel can produce local compression and flame-induced flow redistribution even when downstream pressure relief is available. Three-dimensional compressible reacting-flow simulations are used to examine the flame-head morphology, center-ahead pressure loading, and recessed-center wake motion in a straight channel with one closed end and one open end. Four diagnostics are extracted with a common post-processing framework: flame-head splitting, local center-ahead overpressure, tip–center velocity separation, and wake backflow. The stoichiometric mixture is used as the reference case, and neighboring leaner and richer mixtures test how mixture strength shifts the same response sequence. Under the present half-open confinement, the initially compact flame develops a center-plane-dominant split front. Local compression then appears ahead of the recessed center while branch-tip dominance and negative wake velocity strengthen together. Across the tested mixtures, the richer case enters the coupled response earlier in absolute time, whereas the stoichiometric case retains the strongest late-stage structural response at matched normalized stages. The analysis emphasizes large-scale flame topology, response timing, and inter-case trends under a common numerical closure. The resulting framework links split morphology, local pressure loading, and flow redistribution in half-open premixed reacting-flow configurations.