Numerical simulation of early flame propagation in vented explosions

Gas explosions in semi-confined spaces with obstacles are closely related to industrial and building safety and simulation of such situations are still challenging for modelers. This paper presents the modelling of the influence of ignition and early flame propagation on vented explosion simulations. Numerical simulations using the Large Eddy Simulation (LES) technique have been carried out for a stagnant, stoichiometric propane-air mixture. The test case chosen for the present study is the experiments of small-scale Sydney explosion chamber [1]. In LES, the filtered reaction rate is modelled using a dynamic flame surface density (DFSD) model [2]. Two approaches of computing ignition were studied: 1). use of the main combustion model in an appropriate predefined ignition region, 2). use of a flame kernel model to calculate ignition and initial flame propagation. The aim of this study is to investigate the importance and impact of ignition modelling on the critical parameters for safety assessment, including the maximum generated overpressure, time and location of the peak pressure. Validation against the experimental data shows the appropriateness of the flame kernel model in predicting the initial phase of combustion and the timing of the overpressure history. Results and analysis reveal that a realistic description of the early flame kernel growth is important for FSD related approaches used in modelling a highly unsteady explosion phenomenon.