Simulations of flame-vortex interactions

Abstract

Full numerical simulations are used to study the interaction of a vortex and a premixed flame as a model problem for turbulent flames. A vortex structure is constructed that avoids boundary condition difficulties. The effects of heat release and the importance of the relative length and time scales of the vortex and flame are examined. Changes in the internal structure as well as the overall shapes of the flame and vortex are studied. Frozen flame and frozen vortex cases are studied to isolate various effects and aid in understanding the full interaction. The principal effect of the frozen flame is to expand the vorticity normal to the flame surface. A model using the baroclinic torque is developed to explain this effect. The principal effect of the frozen vortex on the flame is to increase the flame area. This is modeled using the total strain rate associated with the vortex. Important changes in internal flame structure were found to occur only at relatively low Damköhler numbers (Da < 0.5). The full flame-vortex interaction is a combination of the two frozen cases, with additional effects due to flame curvature and to the simultaneous evolution of the flame and vortex. The former results in flame generated vorticity, an effect directly related to the heat release. The latter altered the vortex structure resulting in changes in the pressure field and increased dissipation.