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RR629 - Extension of the dense gas dispersion
model DRIFT to include buoyant lift-off
and buoyant rise

This report concerns the initial specification of equations extending the dense gas dispersion model DRIFT to include buoyant lift-off and rise. The lift-off modelling is based on that for a free buoyant cloud. ‘Added mass’ terms are included in the model’s vertical momentum equation since they offer the prospect of suppressing lift-off for wide clouds. The elevated continuous plume model is chosen to be similar to other published elevated plume models (eg Ott [Risø Report Risø-R-1293EN, Oct 2001], Tickle et al. [AEA Technology Report AEAT/NOIL/27328006/001(R) Issue 2, June 2001]. The elevated instantaneous model is based on the puff model of Turner [J. Fluid Mech. 19, 1964, pp481-491]. The proposed model smoothly evolves between grounded and elevated phases. Passive spreading of the elevated cloud is based on a relative diffusion model [Risø Report Risø-R-1293EN, Oct 2001]. DRIFT’s atmospheric profiles have been extended to above the surface layer and to include profiles of temperature and humidity.

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Updated 2010-03-19