Radial / Tangential Modes of Resonant Oscillatory Combustion in Tubular Flame Burners

Abstract

The radial / tangential modes of acoustically resonant oscillatory combustion have been observed in the large scale tubular flame burners. The triggering and amplification mechanisms of those modes of oscillations can be understood in detail with tubular flame burners because (1) those modes of oscillations have been found to be occurred in tubular flame burners at relatively low thermal input conditions with high reproducibility, and thus, the experiments can be repeatedly conducted under the well-controlled conditions, and (2) the modes of oscillations are easily identified because the natural frequencies of the tubular flame burners are easily obtained due to its simple geometry, and furthermore (3) the heat release position can be easily identified because the tubular flame is the thin laminar flame front. At present, it was found that (n, m) = (0, 1) mode of oscillation which has non-axisymmetric sound pressure profile is the dominant mode of oscillation, where n and m is the radial and tangential mode number, respectively. As results of flow field measurements, the Presessing Vortex Core motion was observed in the burned gas region of the tubular flame burner, which can cause the non-axisymmetric sound pressure structure in the tubular flame burner.