Global stability analysis of line-fire flickering

Abstract eng:
In the present work we investigate the flickering of planar jet diffusion flames as a global instability mode. Our study attempts to give a quantitative description of the dynamics of the unsteady processes observed in line fires, which have recently been shown to play a key role in their spread rate. Because the character of the instability is purely hydrodynamic, the flame can be described in the infinitely fast reaction limit. The analysis permits the determination of the critical conditions, in terms of the Reynolds and the Froude number, for the onset of the global instability, as well as its associated frequency. The analysis is extended to include spatially periodicity in the spanwise direction. It is investigated if there is a spanwise wave number that maximizes the growth rate of the global instability mode, explaining the spanwise undulations with peaks and troughs that prevail in realistic line fires.

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