Numerical investigation of the effect of obstacle shape on deflagration to detonation transition in a hydrogen–air mixture

Abstract

The potential for deflagration to detonation transition (DDT) in an uncontained failure poses extreme risk to nearby personnel. This study performs numerical simulations with detailed chemistry models of confined stoichiometric hydrogen–air mixtures interacting with flow obstructions to better understand the mechanisms of detonation initiation which will inform future risk assessments. Unique obstacle geometries, including both rectangular and curved obstacles, are considered in an effort to isolate important contributors to DDT. Contributors are shown to be pressure wave interactions in unburned fuel and flow features, such as vortical structures, which encourage flame acceleration. In this study, detonation was only observed in cases with sharp-edged obstacles and not in smooth-walled cases. The sharp edges introduced vortex shedding which contributed to flame distortion and resulted in acceleration. In addition, detonation was observed where strong pressure waves and reflections interacted in unburned fuel. The variations in geometry within the sharp-edged obstacles had some effect on vortex shedding and the reflections of generated shocks resulting in small changes in detonation location, however, the mechanism of DDT appeared the same, and the changes were small in comparison to the smooth-walled cases which did not detonate.