Modelling and Large Eddy Simulation of Large-scale Hydrogen-air Deflagration and Deflagration-to Detonation Transition

Abstract

A release of hydrogen in industry could form a highly reactive mixture. Ignition of this mixture and acceleration of the flame due to turbulence and confinement could go for a transition to detonation through a mechanism called deflagration-to-detonation transition (DDT). Detonation produces high overpressure in the order of tens of 푏푎푟, which produces risk for lives and damage to the buildings.
It would be required to numerically study the possibility of explosion and transition to detonation for a safety purpose. The prediction of the flame propagation velocity and overpressure of the explosion does not require resolving flame details. Therefore, flame wrinkling models are suitable candidates for studying industrial scales.
Hence, the aim of the current study is to develop a reliable flame wrinkling model to predict flame deflagration and detonation in the framework of the large eddy simulation. Two main mechanisms responsible for flame acceleration are considered in the current study, which are flame intrinsic instabilities and turbulence. The instabilities mechanism, including the interaction of turbulence, and the turbulence mechanism are separately modelled using the fractal description. A proposed model for the inner cut-off length scale of turbulence is developed, which is suitable for the corrugated flamelets and the thin reaction zones regimes. The effect of excessive stretching to quench the flame is included. For a complete closure of the turbulence modelling, the effect of the flame to generate turbulence is included.
The model is tested against three experiments: DDT in a channel, large-scale deflagration in an open atmosphere, and vented explosion. The DDT simulation predicts good flame propagation velocity compared with the shock propagation velocity of the experiment. The open atmosphere simulation qualitatively predicts flame propagation and overpressure comparable with the experiment and the state-of-the-art (SOTA). The vented explosion simulation qualitatively predicts flame propagation and overpressure in the order of the experiment and the SOTA. Despite, the predicted overpressure is not converged based on the resolutions of the tested meshes.
The overall performance of the model is qualitatively acceptable for simulating deflagration and DDT.

Date of Award	Nov 2020
Original language	English
Supervisor	Sile Brennan (Supervisor) & Neil Hewitt (Supervisor)