Role of Obstacle Orientation in Controlling Flame Acceleration and Detonation Dynamics within Confined Hydrogen-Air.

To assess explosion risks in confined environments, understanding flame acceleration and the deflagration-to-detonation transition (DDT) in hydrogen-air premixed mixtures is essential. The influence of obstacle angle on flame acceleration and detonation initiation is analyzed with large-eddy simulations (LES) within the OpenFOAM framework. The results demonstrate that variations in obstacle angle significantly modify the flow-field structure, thereby affecting both flame acceleration and detonation intensity. Larger angles generate more extensive leeward recirculation zones, which enhance flame wrinkling and stretching, increase turbulence intensity, and promote flame propagation. The DDT process is primarily dominated by the formation and evolution of the leading shock wave. Depending on the obstacle angle, two detonation initiation modes are identified: (i) direct initiation triggered by the interaction between reflected shock waves and the flame front, and (ii) initiation resulting from localized high-pressure regions formed through shock-wave focusing. Despite these differences, all cases conform to the Zel'dovich gradient mechanism. From a safety perspective, larger obstacle angles should be avoided when peak detonation pressure is considered, whereas smaller angles are preferable when initiation time is used as the criterion. When the detonation initiation distance is adopted, an angle of 30° presents the highest potential hazard. These findings provide valuable guidance for the safety design and risk assessment of hydrogen energy systems.