Numerical Study On Flashback In Laminar Boundary Layers

Flashback is the process of flame propagating upstream from combustion zone. Flashback, which is one of the combustion instabilities in the gas turbine and other combustion devices and the most principal and important combustion problems, determines the reliability of the combustion device. This paper reviews the development of the research on flame flashback and the study on the flashback in gas turbine is introduced in detail over the past thirty years, which indicate that as one of the five classical flashback mechanisms, flashback in the wall boundary layer has become one of the most critical problems for the basic research on flashback mechanisms and combustor designs. In view of this, flashback in laminar boundary layer of H2-Air has been studied in detail by numerical simulation using one-step and a 10 species,21-steps H2-O2 mechanism respectively, and a detail analysis on the mechanism of the laminar boundary layer flashback (BLF) has been carried out in the meantime. The results reveal that:1) The increase of equivalence ratio promotes the propagation of flame to upstream; 2) Flame will be changed from stable to flashback with a small increasement of the equivalence ratio in the vicinity of flashback limit, which means that the flame is very sensitive to the changes of equivalence ratio; 3) The single-step mechanism of H2-Air can only qualitatively capture the character of flashback in laminar boundary layer; The features of flashback in laminar boundary layer can be captured very well based on the 21-steps mechanism but with a large amount of computational cost; The Critical Gradient Model(CGM) developed by Lewis can predict the parameters of laminar boundary layer flashback quickly and the results are in good agreement with the calculation; 4) The backflow region is caused by the pressure rise induced by the interaction of flame-flow; 5) The backflow region moves upstream in the form of "recirculation bubble", and the interaction between flame and the "recirculation bubble" promotes the flame propagation upstream in the boundary layer.