The Integral Dense-gas Dispersion Model (IDDM) and comparison with Jack Rabbit II data

• Published in: Atmospheric environment (1994) Vol. 296; p. 119563
• Main Authors: Weil, Jeffrey C., Alessandrini, Stefano
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2023
• Subjects: Dense gas dispersion; Integral cloud model; Internal boundary layer; Jack Rabbit II experiment; Longitudinal shear dispersion; Model evaluation; Model evaluation; Jack Rabbit II experiment; Integral cloud model; Internal boundary layer; Longitudinal shear dispersion; Dense gas dispersion
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2022.119563

The Integral Dense-gas Dispersion Model (IDDM) is presented and used to predict the maximum concentrations and spread of a dense-gas cloud from a short-term release. IDDM is based on integrated conservation equations and includes spreading due to source momentum and density effects, cloud-top air entrainment, height changes with time, and wind transport. The equations are solved numerically but some useful analytical results are found showing the dependence of cloud radius and height on source conditions, entrainment, and time. IDDM comparisons with the Jack Rabbit (JR) II experiments are made for two smooth-terrain Trials (6, 7) and one with a Mock Urban Array (MUA) of Conex containers (Trial 1). For the smooth-terrain cases, predicted concentrations (C) follow the observed JR II data trends with distance x, and for x>1 km are consistent with a -5/3 empirical correlation. In the near field, analytical results for C show excellent agreement with the IDDM numerical solution. For Trial 1, an internal boundary layer (IBL) model is added to obtain the modified winds, friction velocity, and IBL depth due to the MUA. With the IBL and a mean depth (10 m) included, IDDM concentrations agree with the data. Over all Trials (1,6,7), IDDM exhibits good statistical performance with 83% of the predictions within a factor of 2 of the observations. An elliptical horizontal cloud geometry is added to estimate the lateral cloud width given an anisotropy ratio (ani) of along-wind (x) to lateral (y) cloud width. With constant ani (=3), the agreement between predicted and observed width is good with a geometric mean (GM) of predicted-to-observed width of 1.02 and a geometric standard deviation (GSD) of 1.35. However, with a trial-specific ani (=0.5−3) and longitudinal wind shear included, the mean model agreement (GM) is about the same, but the model-data scatter is reduced to a GSD of ≃1.1. •Integral Dense-gas Dispersion Model (IDDM) presented for modeling concentrations of dense-gas cloud.•Cloud spreading caused first by source momentum and then by density effects.•Internal boundary layer model necessary for predictions over Mock Urban Array of shipping containers.•Elliptical horizontal cloud model and wind shear improve lateral width estimates.•IDDM predictions within factor of 2 of Jack Rabbit II chlorine concentrations in 83% of comparisons.