- Author
- Floyd, J. E.
- Title
- Large Eddy Simulation of Compartment Fires Using a Mixture Fracture Combustion Model. BFRL Fire Research Seminar. VHS Video.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
- Video, February 13, 2001,
- Keywords
- combustion models | compartments | predictive models | simulation
- Abstract
- The simulation of fires using computational fluid dynamics (CFD) is challenging because for most cases of interest it is too expensive to use a computational grid fine enough to resolve the combustion process directly. A relatively inexpensive method preserving some of the combustion chemistry assumes that fuel and oxygen react infinitely fast. With this assumption, all that is required of the calculation is to track a single scalar quantity that represents the fraction of material originating as fuel. This quantity, referred to as the mixture fraction, obeys the same conservation equations as the individual gas species typically tracked in a combustion calculation. >From the mixture fraction, mass fractions for all other species can be derived based on empirical state relationships. Typically, in a mixture fraction-based combustion model the reaction takes place on an infinitely thin flame sheet where both the fuel and oxygen concentrations go to zero. To avoid having to resolve the actual flame itself, the traditional model is modified resulting in a reaction zone of finite thickness. These modifications preserve the chemistry of the original state relationships and they provide a framework for the future inclusion of minor combustion species such as carbon monoxide. A mixture fraction combustion model has been added to FDS and is validated against experimental data from a large scale fire experiment in a decommissioned, German, nuclear power plant. Results of the new combustion model are also compared against those from the previous model.