Dynamics of premixed swirl flames under the influence of transverse acoustic fluctuations

Flame dynamics in the presence of transverse acoustic fluctuations is an aspect of relevance to modern annular combustors. In particular, it is a key element underlying the occurrence and characteristics of thermoacoustic instability in annular combustors, which primarily involves azimuthal acoustic modes. In this paper, we present our experimental investigation of the response of a generic swirl-stabilized premixed flame to various transverse acoustic forcing configurations. Experiments were performed on a single burner rig featuring a combustor with transverse extensions. The flame was subjected to transverse acoustic fluctuations by generating controlled standing acoustic modes in this combustor. Two main results constitute this study: First, the obtained results reveal that flame response to transverse acoustic pressure fluctuations is quantitatively different when compared to axial forcing for low frequencies. Second, transverse acoustic velocity affects flame response to axial forcing such that the effects are dependent on the amplitude of transverse velocity fluctuations, the phase difference between axial and transverse forcing, and the inherent asymmetry of the flame.