Lift-off and blow-out of under-expanded hydrogen jets: experiments versus simulations

Turbulent non-premixed flame stability limits are very important for safety considerations, especially for design of thermally activated pressure relief devices (TPRD), e.g. to prevent flame blow-off and hydrogen accumulation in the enclosure. There is a body of research on parameters of lift-off and blow-out for turbulent non-premixed flames. Hydrogen safety engineering requires validated contemporary tools, such as CFD models, that can be used for the design of TPRD, which parameters will provide either the stabilisation of flame or its blow-off, including the effect of wind. The applied in this study CFD model is based on the eddy dissipation concept (EDC) sub-model for combustion, which incorporates a detailed chemistry mechanism with 37 chemical reactions, and the RNG k-epsilon sub-model for turbulence modelling. The model has been successfully applied to simulation of spontaneous ignition during the sudden release of hydrogen into the air, and the numerical study of indoor jet fire regimes. The notional nozzle theory for under-expanded jets is applied as a part of the CFD modelling approach. It is proved to be able to reproduce lift-off and blow-off phenomena that were observed in experiments, with reasonable computational consumption, i.e. CPU time of 6 hours on 64 cores. The model gives insights into the dynamics of the lift-off and blow-off phenomena. The simulations reproduced exactly experimental results on transition from lift-off (0.4 mm nozzle) to blow-off (0.3 mm nozzle) at storage pressure of about 10 MPa.