Effect of Flammable Cloud Treatment On Predicted Blast Loads

Computational fluid dynamic (CFD) analysis of flammable gas dispersion can provide a realistic evaluation of the resulting flammable gas cloud. CFD dispersion analysis can provide a more realistic assessment of the resulting gas cloud in heavily congested and/or confined environments relative to simplified dispersion analysis methods. In contrast to simplified methods, the gas cloud predicted using CFD analysis in congested/confined environments is typically complex, both in terms of shape and concentration gradients. The blast loads predicted using CFD vapor cloud explosion (VCE) analysis for the resulting flammable gas cloud are dependent upon the representation chosen for the gas cloud. Directly utilizing the predicted dispersed gas cloud, with the corresponding complexities in shape and concentration gradients, requires an extended series of analyses, since both ignition location within the cloud and the cloud location can have a strong influence on the predicted blast load. A common approach is to replace the dispersed gas cloud with a simplified representation for the purposes of performing a CFD VCE blast load assessment, such as a cubic shaped cloud with a uniform near-stoichiometric fuel concentration. This approach is very attractive since it greatly simplifies the blast load assessment. However, the relationship between the blast loads predicted using a simplified cloud representation versus those predicted for the actual dispersed cloud is not well defined.