Journal of Propulsion and Energy ISSN:2734-1887(Print) 2765-0049(Online)

When several swirl-stabilized flames are narrowly spaced in a low-emission gas turbine combustor, neighboring flames will interact. Understanding the response characteristics of the interacting flames is essential to control the development of self-excited combustion dynamics. The present study is concerned in particular with the influence of swirl flow parameters – relative rotational direction and swirl number combination – on the system’s thermoacoustic response. Phase-resolved CH* chemiluminescence imaging, OH Planar Laser Induced Fluorescence (PLIF), acoustic pressure, and global heat release rate measurements were performed to study the flame dynamics subjected to co-rotating and counter-rotating swirl arrangements with symmetric and asymmetric swirl number distributions. These parameters were found to exert a remarkable influence on the development of self- excited combustion instability. Our results suggest that counter-rotating swirl configurations, in which adjacent tangential streams flow in the same direction in the interaction region, are more effective to limit the growth of the instability for all swirl number combinations. Instantaneous flame front images reveal that the counter-rotating swirl flame interaction causes the two adjacent flames to stabilize in both the inner and outer shear layers, leading to the formation of the well-known “M” structure. By contrast, the interaction induced by co-rotating swirl flow tends to disturb the flame anchoring at the outer shear layers of each flame, due to the emergence of a large-scale flame front deformation, even under unforced conditions. Impingement of two opposed tangential jets is thought to be linked to the generation of disturbances, which in turn affect stabilization mechanisms and the dynamics of two interacting swirl flames.