Prediction of Lifted Diffusion Flames by using the Scalar Field Variable.

Abstract

By incorporating the scalar field variable, G, into the numerical method with the flame sheet model, one of reaction models of simulation of diffusion flames, we have developed a new calculation method of lifted flames. The present method can deal with the flame instabilities including the blowoff, liftoff, and extinction, while the conventional flame sheet model cannot deal with them, because scalar quantities are decided uniquely against the mixture fraction in that model. The burning velocity included in the production term of the equation of scalar field variable, G, is formulated as a function of the scalar dissipation rate. This makes the treatment of the flame instabilities possible. The frozen scalar structure is applied to the upstream of the intersection of isolines of the stoichiometric line and G=1, the transitional structure expressed by a weight function based on the scalar field variable, G, to a small zone behind the intersection, and the diffusion flame structure to the downstream region. Numerical results of a reactive two dimensional mixing layer by the present method are in reasonable agreement with results of direct numerical simulations with a finite reaction rate and irreversible one step reaction model.