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Conference Papers Year : 2010

Dispersion in confined building : a coupled approach


Modelling gas dispersion in mechanically ventilated building is a challenge for safety engineers. A leak in such an infrastructure can generate two different consequences: toxic effect or blast effect after a flammable vapour cloud ignition. In both case, it is important to be able to predict the gas behaviour using numerical tools in order to be able to design adapted ventilation systems. Gaseous products are generally stored under pressure that induces high velocity in case of release from the tank or following a line rupture. Considering this important pressure, the jet zone is a highly complex zone with a Mach number higher than 1 that induces shock waves. These waves correspond to discontinuity of the flow. After this jet zone, a transition region (air entrainment) is observed and can be characterised by the beginning mixture of the gas with air. This also corresponds to an expansion of the jet diameter inducing a velocity decrease. Finally, after this zone, the flow becomes governed by the ventilation system where the Mach number is lower than 1. To model gas dispersion in closed enclosure, CFD models can be used. Such codes enable to predict the different physical quantities in the whole domain along time. However, most of these codes are not able to model complex phenomena such as ones that characterised the jet region. CFD codes are able to capture such a complex physic require mesh in the jet zone that is not in accordance with the objective to model the whole infrastructure considering current computing limitations. To overcome this and making achievable such modelling, a coupled approach between a 1D jet model and a CFD code is proposed. The 1D model predicts gas behaviour in the jet zone while the CFD code describes the concentration and velocity in the whole domain. The FDS CFD code was used. This code is based on the LES approach for turbulence modelling. Such an approach is highly interesting for safety because it enables not to predict an average configuration but a realistic one. Because of the well known capability of this code for predicting smoke behaviour considering ventilation, it is useful to wonder about its capability to model gas dispersion in buildings. A comparison between FDS, coupled with the 1D model, results and experimental ones are given. The experimental results were obtained in an 80 m3 room equipped with a ventilation system in which ammoniac was injected. Two different ventilation regimes were used and concentrations were measured in several locations inside the room at different heights. Comparisons between experimental and numerical values shows a great agreement and leads to the conclusion that the FDS code is a pertinent tool for gas dispersion modelling in confined building when coupling this code with a 1D jet model.
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ineris-00973597 , version 1 (04-04-2014)



Benjamin Truchot, Stéphane Duplantier. Dispersion in confined building : a coupled approach. International Symposium on Safety Science and Technology 2010 (ISSST 2010), Oct 2010, Hangzhou, China. pp.1239-1250. ⟨ineris-00973597⟩


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