Numerical Simulation of Fire Growth, Transition to Flashover, and Post-Flashover Dynamics in the Dalmarnock Fire Test MARIANO LAZARO 1 , HAVARD BOEHMER 2 , DANIEL ALVEAR 1 , JORGE A. CAPOTE 1 and ARNAUD TROUVE 2 1 Group GIDAI University of Cantabria Santander 39005, Spain 2 Department of Fire Protection Engineering University of Maryland College Park, Maryland 20742, USA ABSTRACT The objective of the present study is to evaluate the ability of current Computational Fluid Dynamics (CFD) tools to simulate compartment fires with flashover followed by under-ventilated and/or quasi- stoichiometric, partially-under-ventilated conditions. Current CFD capabilities are illustrated using the Fire Dynamics Simulator (FDS, Version 5), developed by the National Institute of Standards and Technology, USA. The FDS modeling capability is evaluated by detailed comparisons with an experimental database previously developed by the University of Edinburgh, UK. The test configuration corresponds to a full- scale fire test known as the Dalmarnock fire test (test 1). The description of the flammable content in the fire room is based on a standard modeling approach in which the ignition time of flammable objects and materials is calculated using a local heat transfer solver, while the fuel mass loss rate after ignition is prescribed using experimental data from cone/furniture calorimeter tests. The simulated Dalmarnock fire scenario includes flashover, a first post-flashover stage that is under-ventilated and characterized by burning outside the fire room, and a second post-flashover stage that is partially-under-ventilated and characterized by distributed burning inside the fire room. Transition to this second stage is triggered by window breakage in the fire room. The different stages of the fire scenario are analyzed in terms of the fire room global equivalence ratio (GER), which is considered as the main controlling parameter of the fire behavior. Comparisons between numerical results and experimental data are relatively good when considering the global features of the fire dynamics, e.g., the time history of the spatially-averaged heat release rate. Comparisons are not as good when considering local features, e.g., the time history of gas or wall temperatures, or that of wall heat fluxes. KEYWORDS: fire modeling, CFD, fire growth, compartment fires, flashover, post-flashover, global equivalence ratio, Dalmarnock. INTRODUCTION Compartment fires exhibit unique features associated with the presence of multiple/complex fuel sources, smoke accumulation, restricted air ventilation, and interactions between flames and solid walls [1-3]. A typical compartment fire scenario evolves through a succession of stages, for instance: an ignition stage corresponding to the thermal degradation of an initial fuel source, followed by the start of flaming combustion and the early fire growth; a pre-flashover stage featuring a well-ventilated (i.e., fuel-limited) fire and a growing hot smoke layer near the compartment ceiling (this layer contributes in turn to the intensification of heat exchanges − in particular thermal radiation exchanges − and promotes faster fire growth); a flashover stage that corresponds to a series of spontaneous ignition events driven by high irradiation levels from super-hot ceiling layer gases (i.e., gases with temperatures in excess of 800-900 K) and results in a full involvement of all flammable contents in the fire room; a post-flashover, fully- developed stage featuring a ventilation-controlled (i.e., oxygen-limited) fire and often resulting in external burning and fire spread from the room of fire origin to adjacent compartments. An important parameter that characterizes the compartment fire behaviour is the global equivalence ratio (GER). GER is defined as the averaged fuel-to-oxygen mass ratio in the fire room divided by its stoichiometic value. Note that the stoichiometric value of the fuel-to-oxygen mass ratio may not be known or even well defined in a real-world compartment fire scenario (because of both the heterogeneity of the fuel sources and the unknown chemical composition of the fuel vapors); in that case GER cannot be 1377 FIRE SAFETY SCIENCE–PROCEEDINGS OF THE NINTH INTERNATIONAL SYMPOSIUM, pp. 1377-1388 COPYRIGHT © 2008 INTERNATIONAL ASSOCIATION FOR FIRE SAFETY SCIENCE / DOI:10.3801/IAFSS.FSS.9-1377