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Fire Technology, 45, 323340, 2009 2008 Springer Science+Business Media, LLC. Manufactured in The United States
DOI: 10.1007/s10694-008-0066-4
Christian Perez-Jimenez*, LABEIN-TECNALIA S.A.I., Bilbao, SpainGeorges Jan Guigay, Bjorn Karlsson and Jonas Eliasson, Iceland Fire Authority,
Reykjavik, IcelandAndrej Horvat, Intelligent Fluid Solutions, London, UK Yehuda Sinai, ANSYS UK Ltd., Sheeld, UK Jean-Marc Franssen, University of Liege, Liege, Belgium
Received: 8 November 2006/Accepted: 22 August 2008
Abstract. The phenomenon of backdraft is closely linked to the formation of a ammable region due to the mixing process between the unburned gases accumulated in the compartment and the fresh air entering the compartment through a recently created opening. The ow of incoming fresh air is called the gravity current. Gravity current prior to backdraft has already been studied, Fleischmann (1993, Backdraft phenomena, NIST-GCR-94-646. University of California, Berkeley) and Fleischmann (1999, Numerical and experimental gravity currents related to backdrafts, Fire Safety Journal); Weng et al. (2002, Exp Fluids 33:398404), but all simulations and experiments found in the current literature are systematically based on a perfectly regular volume, usually parallelipedic in shape, without any piece of furniture or equipment in the compartment. Yet, various obstacles are normally found in real compartments and the question is whether they aect the gravity current velocity and the level of mixing between fresh and vitiated gases. In the work reported here, gravity current prior to backdraft in compartment with obstacles is investigated by means of three-dimensional CFD numerical simulations. These simulations use as a reference case the back-draft experiment test carried out by Gojkovic (2000, Initial Backdraft. Department of Fire Safety Engineering, Lunds Tekniska Hogskola Universitet, Report 3121). The Froude number, the transit time and the ignition time are obtained from the computations and compared to the tests in order to validate the model.
Keyword: gravity current, 3-D simulation, obstacles, backdraft, ignition time
Nomenclature
B Width of the container (m)
C Drag coecient of the obstacle Fr Froude numberF Force (N)g Gravity (m/s2)
h Height of the obstacle (m)h* Non-dimensional height of the gravity currentho Height of the gravity current measured over the distance 3L/4 to L (m)
* Correspondence should be addressed to: Christian Prez-Jimnez, E-mail: [email protected]
Inuence of Obstacles on the Development of Gravity Current Prior to Backdraft
324 Fire Technology 2009
h1 Height...