A numerical study of backdraft dynamics using a level-set nonadiabatic flamelet model

Abstract

The backdraft dynamics are numerically investigated using a proposed combustion model that attempts to accurately simulate the multi-combustion regime with a fast flame propagation in the inhomogeneous thermal condition. This scenario is often found in the limited-ventilation fires. The modeling strategy includes the flame-front tracking by the level-set function and the solution of non-adiabatic flamelet and a stratification parameter. In a comparison to the previous works, the present approach shows a better agreement with experiments. The results also underline the important effect of gravity current that promotes the rapid flame evolution in the case with less-dense initial mixture. Four different phases are identified based on the transient characteristics of backdraft, and they are (a) initial ignition, (b) free propagation, (c) limited-front propagation and (d) accumulation & flame-ejection. The dominant driving forces of buoyancy convection and turbulence effect on burning velocity are revealed. The backdraft process is found to encompass the initial premixed flame propagation and the diffusion burning outside the chamber following the formation of fireball. This work gains the valuable insights on the backdraft dynamics and provides useful information to design effective protection measures.

Keywords

• backdraft
• large-eddy simulation
• level-set function
• mixed combustion regime
• burning velocity