Impact of Wall Roughness on the spontaneous ignition of pressurized hydrogen released into a tube

Abstract While significant advancements have been made in understanding the spontaneous ignition of pressurized hydrogen during accidental releases, the aerodynamic effects of tube surface conditions remain critically underexplored. This paper presents a numerical investigation into the effects of equivalent sand-grain wall roughness (Ra) on the ignition mechanisms, shock wave propagation, and non-premixed flame evolution of pressurized hydrogen releases. Utilizing Large Eddy Simulation (LES) coupled with a mixture averaged transport model and an Improved Partially Stirred Reactor (PaSR) combustion model, the study evaluates the transient dynamics across absolutely smooth (Ra = 0 mm) and varying rough (Ra = 0.1, 0.5, 1.0 mm) tube boundary conditions. The analysis demonstrates that wall roughness significantly suppresses the radial expansion and central coalescence of the flame front, ultimately leading to the dissipation of the central reaction zone at high roughness scales. Conversely, roughness-induced localized vortices drastically intensify boundary layer combustion. Furthermore, wall roughness introduces a non-linear suppression of leading shock wave velocities and elevates the critical burst pressure threshold required for spontaneous ignition from 3.2 MPa to 3.5 MPa, driven by intense near-wall momentum and thermal dissipation. The findings provide critical theoretical foundations for the quantitative risk assessment of hydrogen infrastructure and inform future iterations of tube safety standards.