Validation of CFD-model for hydrogen dispersion

To be able to perform proper consequence modelling as a part of a risk assessment, it is essential to be able to model the physical processes well. Simplified tools for dispersion and explosion predictions are generally not very useful. CFD tools have the potential to model the relevant physics and predict well, but without proper user guidelines based on extensive validation work, very mixed prediction capability can be expected. In this article, recent dispersion validation effort for the CFD tool FLACS–HYDROGEN is presented. A range of different experiments is simulated, including low-momentum releases in a garage, subsonic jets in a garage with stratification effects and subsequent slow diffusion, low momentum and subsonic horizontal jets influenced by buoyancy, and free jets from high-pressure vessels. LH₂ releases are also considered. Some of the simulations are performed as blind predictions.     

Modelling large-scale vented gas explosions in a twin-compartment enclosure

Natural gas and LPG are common fuels that have been used relatively safely in the home for many decades. However, when there is a release of gas within a dwelling, or gas from a leaking external pipeline migrates into a building, an explosion may occur. Most of the experimental research into vented gas explosions has been conducted in single enclosure, cuboid or spherical geometries which are not representative of accidental explosions in dwellings or process industries. This paper discusses the findings of a comprehensive large-scale experimental programme undertaken by British Gas Research and Development and also compares FLACS CFD (Computational Fluid Dynamics) simulations against a number of these experiments. The results suggest that the software is useful in gaining a greater understanding of the dynamics of explosion development in dwellings. The paper highlights areas of good performance of the software as well as areas of shortcomings where further understanding and modelling effort is needed.