Controlled Numerical Assessment of Near-Equal-Inventory Hydrogen–Air Redistribution Effects on Early Flame and Pressure Responses in a Semi-Open Narrow Channel

Redistributing a nearly fixed hydrogen–air inventory can alter early flame response under confinement, while terminal-state comparisons may confound mixture placement with unequal flame development. Three-dimensional WALE–PaSR calculations in a 0.240×0.020×0.020m semi-open channel compare eight redistribution archetypes whose hydrogen and oxygen inventory mismatches do not exceed 0.385% and 0.011%, respectively. Cases are aligned over χ=0.05–0.15 using flame-front speed, whole-domain gauge pressure, positive heat-release, hydrogen-consumption, and wake/backflow diagnostics. The common-window front speed spans 26.5–62.3ms−1, while the monitored responses do not collapse onto one trajectory. A one-dimensional check using the same 10-species/27-reaction mechanism differs from the Dayma–Halter–Dagaut experimental values by at most 6.85%. Selected grid, maximum-Courant-number, and PaSR perturbations, together with representative positive-Sutherland AX-I/U10 calculations, bound numerical and transport-model sensitivity. For that pair, the response direction is retained for front speed, instantaneous whole-domain maximum gauge pressure, and the domain-integrated positive heat-release-rate indicator, whereas the domain-mean pressure contrast remains within the selected 6% interpretive envelope. Spatial redistribution is therefore supported as a model-bounded screening variable, not as facility-level validation, a universal severity ranking, or safety certification.