EFFECT OF SWIRLING NUMBER AND DIRECTION ON FLAME MORPHOLOGY AND COMBUSTION PERFORMANCE IN A CENTRALLY STAGED SWIRL COMBUSTOR

Swirl flow is a prominent technology for effectively controlling combustion stability, combustion intensity, and various other aspects in a gas turbine combustor, while the interaction between the two stages of the swirler affects the flame morphology within the recirculation zone, subsequently influencing the combustion performance. In the present work, focusing on the interaction between the main and pilot stages of the swirler, as well as the regularity that influences the combustion flow field, experimental research and numerical simulations are conducted in the single-sector centrally staged model combustors with different swirling numbers and directions of the pilot stage, while the swirling parameters of the primary stage remain constant. Under constant operating conditions, the flow characteristics of the combustion flow field, the development of high-temperature zones, the evolution of flame morphology, and variations in combustor performance are analyzed. The above analysis is carried out with the swirling numbers of the pilot stage respectively maintained at 0.44, 0.55, and 0.68, as well as the swirling direction of the two stages set as either identical or opposite. Simultaneously, the flame cooperation mechanism between the main and pilot stages is explored. Flame within the combustors exhibit stratified structure. Under a constant swirling direction, changing swirling number causes a variation in opening angle between inner shear layers, then altering fuel distribution, opening angles of flames, as well as confluence between inner and outer main flames. In co-swirl condition, as swirling number of pilot stage increases, total pressure losses rise while PF decreases. Effect of swirling direction combination on PF varies across different swirling numbers of pilot stage. At a swirling number of 0.44, counter-swirl results in a slightly lower PF than coswirl. Nevertheless, at swirling numbers of 0.55 and 0.68, co-swirl proves more effective in achieving lower PF.