Triple flame structure and dynamics at the stabilization point of an unsteady lifted jet diffusion flame

Abstract

We present results of a numerical study of a forced lifted laminar two-dimensional jet flame using a single-step irreversible global mechanism with particular emphasis on the structure and dynamics of the flame base. A coupled Lagrangian-Eulerian low Mach number numerical scheme was developed to solve the governing equations. Finite difference discretization was used with adaptive mesh refinement for the scalar conservation equations, while the vortex method was adopted for the momentum equation. The flame base stabilized in a region where the flow velocity was sufficiently small, and there was adequate premixing of the fuel and oxidizer streams. A triple flame was observed at the flame base and was studied with respect to its global structure, dynamics, and modulation by an unsteady vortex-generated strain field. We studied the unsteady flow field and heat release rate of the flame base as it was entrained, stretched, and contorted by the passing vortex before returning to the original configuration at the termination of the interaction. We observed stretching of the rich triple flame branch associated with the entrainment and isolation of a pocket of coflow air in the jet. We correlated velocity and strain-rate fluctuations at the flame base with changes in peak heat release rate. Given the size of the triple flame, neither the dilatational nor the temperature field were found appropriate for experimental measurement of the triple flame.