Numerical Prediction of Lean Premixed Hydrogen Deflagrations in Vented Vessels

In water-cooled nuclear power plants, hydrogen gas can be generated by various mechanisms during an accident. In case combustion of the resulting hydrogen-air mixture within the facility occurs, existing containment structures may be compromised, and excessive radio-active material can be released to the environment. Thus, an improved understanding of the propagation of lean hydrogen deflagrations within buildings and structures is essential for the development of appropriate accident management strategies associated with these scenarios. Following the accident in Fukushima, Japan, the application of three-dimensional computational fluid dynamics methods to high-fidelity detailed analysis of hydrogen combustion processes in both closed and vented vessels has become more widespread. In this study, a recently developed large-eddy-simulation (LES) capability is applied to the prediction of lean premixed hydrogen deflagrations in vented vessels. The LES methodology makes use of a flamelet- or progress-variable-based combustion model coupled with an empirical burning velocity model (BVM), an anisotropic block-based adaptive mesh refinement (AMR) strategy, an accurate finite-volume numerical scheme, and a mesh independent subfilter-scale (SFS) model. Several different vessel and vent sizes and configurations are considered herein. The LES predictions are compared to experimental data obtained from the Large-Scale Vented Combustion Test Facility (LSVCTF) of the Canadian Nuclear Laboratories (CNL), with both quiescent and turbulent initial conditions. Following descriptions of the LES models, LES results for both variable chamber sizes and single- and double-vent cases are presented to illustrate the capabilities of the proposed computational approach. In particular, the predicted time histories of pressure as well as the maximum overpressure achieved within the vessels and combustion compartments are compared to those from the LSVCTF experiments. The influences of the modelled ignition process, initial turbulence, and mesh resolution on the LES results are also discussed. The findings highlight the potential and limitations of the proposed LES approach for accurately describing lean premixed hydrogen deflagrations within vented vessels.