Abstract
A subgrid scale (SGS) model for partially premixed combustion has been implemented and applied to simulate the backdraft phenomena and its mitigation by watermist. The model is based on the coupling of independent approaches for non-premixed and premixed turbulent combustion. The "flame index" concept was used to separate the two different combustion regimes. This index describes the structure of the flame based on fuel and oxygen gradients. By using this approach, it is possible to implement individually the most suitable combustion models for each structure. In the current study, the Large Eddy Laminar Flamelet Model (LELFM) was used for non-premixed combustion and the flame surface density approach for premixed combustion. Simulations were conducted for the reduced scale backdraft tests of Weng and Fan. The predicted pressure-time curve is in good agreement with the measurement The predicted mass flow rate versus time has also captured the correct trend indicated by the measurement but quantitatively relatively larger discrepancies are found. For the simulation with watermist, a correlation for the laminar burning velocity of the methane-air-diluent-water vapor system was introduced following Stone and Clarke and Liaio et al.. In line with the experimental observation, the watermist was found to have mitigated the backdraft by reducing the prevailing laminar flame velocity, resulting in lower temperature and pressure distributions within the compartment However, in this particular case, the mist did not completely suppress the turbulent deflagration. Further study to optimize the mist injection time, speed, quantity, and direction is needed to achieve this goal.