CFD Study of Gas Dispersion and Jet Fires in Complex Geometries

An implementation and validation of a gas dispersion model and a radiation model in the Computational Fluid Dynamics (CFD) code EXSIM (Sæter 1998, Hjertager et al. 1992) have been performed. The extended code is named FLEXSIM (Fire Leak Explosion Simulator). The computational simulations have been performed with different wind speeds, geometries, gas types, release directions, leak rates, and discharge orifices. Results have been validated against experimental findings.

A computational study of air changes and jet leaks, using a buoyant neutral gas, in highly confined and congested geometries has been performed. The results have been compared to large scale experimental findings (Savvides et al. 1999, BG Technology & Shell Global Solutions April 1999). The pre-release ventilation rates are in good quantitative agreement with experiments and well within the criteria for acceptable performance.

The predicted flammable gas volumes show an acceptable quantitative agreement with the majority of the measurements within a factor of two. The flammable gas volumes inside the module are in general over predicted but show an acceptable overall quantitative statistical performance. Two simulations with decaying release rate have been simulated and show good agreement with experimental findings.

A series of buoyant gas releases have been simulated and compared to experimental findings (Roberts et al. 2006, Shell Global Solutions 2003). The releases were performed with methane and hydrogen. The methane releases were over predicted and the hydrogen releases were under predicted. The predicted results are in the high end of acceptable performance.

A numerical study of open field dense gas dispersion has been performed. The predicted transient development compares quantatively well with experimental results (Hall 1997, McQuaid & Roebuck 1985) and (Sklavonuos & Rigas 2004).

The Composite Radiosity Gap radiation model has been implemented in EXSIM. The predicted heat fluxes obtained from horizontally released natural gas jet fires have been compared to experimental findings reported by Johnson et al. (1994). The radiation levels are slightly under predicted but compares qualitatively well with measurements.