The influence of a linear hydrogen concentration gradient on flame acceleration and deflagration-to-detonation transition in obstacles

This study investigates the influence of a linear hydrogen concentration gradient on flame acceleration and deflagration-to-detonation transition (DDT) within obstructed environments. This study employs numerical simulation methods to model the hydrogen flame propagation by coupling turbulence modeling with detailed chemical kinetics. The numerical framework accurately captures the coupled heat transfer behavior using the Euler time integration scheme with the HLLC flux scheme. A baseline hydrogen concentration of 30 vol% is established, featuring linear vertical concentration gradients characterized by slopes of 130.91, 205.72, and 480.00. The simulation results demonstrate that combustion reactions proceed more rapidly in high-concentration regions. This accelerated reaction rate, coupled with boundary layer instability effects, generates localized pressure and temperature gradients that subsequently enhance flame propagation velocity. The characteristic behavior manifests as an increased frequency of flame oscillation and acceleration with higher concentration gradient slopes. This relationship suggests a direct coupling between mixture stratification intensity and combustion instability. Furthermore, while the overdrive detonation velocity exhibits a positive correlation with the gradient slope, the stable detonation velocity remains relatively consistent, being primarily governed by the overall hydrogen concentration.