Interaction of a vortex ring with a diffusion flame
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The interaction between a laminar vortex ring and a flat diffusionflame is investigated via direct numerical simulations. The diffusionflame is generated by a “spark” and is implemented as initial condition for the simulations. The chemistry is modeled by an Arrhenius, single step, irreversible reaction. A heat-releasing flame sheet is also considered in addition to the finite rate flames. The vortex ring is generated by an axisymmetric discharge of fuel-inert species mixture that enters a quiescent medium with the same composition and temperature. Two stages are identified during the finite rate diffusion flame–vortex ring interaction. The first stage corresponds to the head-on collision between the flame and the vortex ring, and lasts until the flame is quenched near the centerline. The unsteady effects are dominant and examination of the terms in the temperature transport equation reveals that, depending on the relative strengths of the vortex ring and the flame,convection and/or diffusion terms are responsible for the local flameextinction. The extinction patterns obtained from the flame–vortex ring interaction during this stage, are compared with the results from unsteady counterflow diffusionflame simulations. The second stage corresponds to the passage of the ring through the flame and its interaction with the flame from the oxidizer side. During this stage, the vortex ring loses its strength and, in addition to the unsteady effects, curvature effects can also become important.