An Experimental Approach to Vortex-Flame Interaction in Practical Turbulent Fields

点击翻译按钮获取中文摘要

In this investigation the processes of vortex-flame interaction of a spark-ignited flame with either coherent structure in the plane premixed shear flow or Karman vortex street in the wake behind a fine cylindrical rod array are experimentally examined, in order to clarify effects of adjacent eddies on the vortex bursting. Propane-air mixture is used in this investigation with an equivalence ratio varied. The results obtained are summarized as follows.(1) In case of the spark ignition at the center of a large scale organized eddy, a flame propagates faster in the axial direction than in the radial one, indicating that the vortex motion enhances the propagation velocity. After completing combustion within an eddy, a pair of flames protrude to adjacent boundary regions on upstream and downstream sides and propagate in the flow direction. The propagation velocity is promoted by the rolling-up motion inherent in the shear flow. In case of the spark ignition at the boundary between adjacent eddies, a flame extends along the contact surface between two mixture streams and becomes S-shaped. It is found that the flame velocity in the flow direction is almost equal to that in the axial direction. When the tips of S-shaped flame reach adjacent eddies, the vortex bursting again enhances the axial flame propagation. It is concluded that there exist two kinds of vortex-flame interactions; one is the vortex bursting, the other is the vortex boosting, and that combination of these two enhancement mechanisms constitutes one of the key factors to the turbulent combustion.(2) A spark-ignited young flame generated in the mixture wake behind a fine cylindrical rod array suffers from the intense cooling and stretching by multiple attacks of Karman vortex. The vortex-flame interaction, therefore, can not always augment flame propagation, but lead to flame extinction in the weak mixture.