Modelling of dispersion of two-phase releases: Part 2 - Numerical solution scheme and validation

Part 1 of this pair of papers described a methodology for modelling the release and dispersion of single- and two-phase materials into the atmosphere. In this paper, the numerical scheme used to solve the governing equations is described and the results generated by the code (named CLOUD) are discussed. The predictions of the code are then compared with results from a number of large-scale experiments involving the dispersion of heavy gases and two-phase jets. Good agreement between the CLOUD results and the experimental data has been found. Sensitivity analyses have shown that, for an upwardly directed or elevated release, the trajectory taken can be sensitive to the correlations used for entrainment of air or for the rainout fraction. For example, with a high entrainment of air, the code may predict that the plume will be buoyant and follow an upward path, whereas with a lower value, a denser plume may result which will quickly fall to the ground, leading to qualitatively different results. It has also been found that if there is a strong exothermic heat of mixing between the released material and water, the trajectory can be heavily dependent on the atmospheric humidity.