Optical and Numerical Analyses of Vortex-Flame Interaction Using Simultaneous and Two-Directional High-Speed Schlieren Photography and Discrete Vortex Method

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The behavior of the propagating flame after the spark ignition in the plane propane-air premixed shear layer is first observed in this paper by combining the following two devised techniques; the acoustic excitation of the plane shear layer and the simultaneous and two-directional schlieren system. To obtain characteristic flame appearances due to the vortex-flame interaction in the plane premixed shear layer, another special idea of assigning two extreme points of ignition is introduced; one at the center of an organized eddy where the vortex motion plays an important role, and the other at the midpoint between two adjacent organized eddies where the rolling-up motion prevails. The two-dimensional change of flame outlines after the midpoint ignition is also simulated by superposing the flame movement with a constant burning velocity followed by thermal expansion on the two-dimensional vortex flow field described by the discrete vortex method. The results obtained are summarized as fol … More lows.(1) It is found that two types of the enhancement mechanisms of flame propagation exist among the organized eddies in the plane shear flow; one is the vortex bursting due to the vortex motion, the other is the vortex boosting due to the rolling-up motion, and exert quantitatively almost the same influences on the flame propagation enhancement process. Also found is that the vortex boosting which is one of the two configurations of vortex-flame interactions can be qualitatively captured by the proposed discrete vortex method.(2) The simulated lateral flame propagation velocities agree relatively well with the axial and lateral flame propagation velocities experimentally obtained from the simultaneous and two-directional high-speed schlieren images, although neglect of the combined effects of the baroclinic torque, the three dimensionality of vortex-flame interaction and the flame curvature leads to slight overestimation of the flame propagation velocity. This result verifies that the proposed two-dimensional discrete vortex method combined with Huygens' Principle is useful for qualitatively estimating and modeling the flame propagation velocity in the plane premixed shear layer, in spite of many assumptions introduced to simplify the numerical simulation.(3) The enhancement effects of flame propagation in the plane premixed shear layer are composed of the physical one due to the vortex-flame interactions and the chemical one through the laminar burning velocity. For both configurations of the vortex-flame interactions, the flame propagation velocity V_f with vortex interaction in the plane premixed shear layer is given by the vortex tangential velocity v_θ plus the propagation speed of the undisturbed flame (ρ_u/ρ_b)S_L, and expressed by the following simple linear equation.V_f=v_θ+(ρ_u/ρ_b)S_L Less