The effects of flame-coupling on exit temperature distribution in a centrally-staged combustor

Hot streak formation, which compromises turbine durability, is a critical challenge in gas turbine combustors, particularly for modern low-emission Lean Premixed Prevaporized (LPP) designs with minimal dilution air. The degree of coupling between staged flames significantly influences these hot streaks. This study experimentally and numerically investigates the impact of flame coupling on exit temperature distribution in a centrally-staged LPP model combustor. Variations in key design parameters— main stage axial velocity and pilot flare angle —were employed to systematically modulate the interaction between pilot and main flames for revealing the underlying mechanisms linking internal flame coupling to the exit temperature profile. Exit temperature distributions were measured and quantified using the Overall Temperature Distribution Factor (OTDF) and Radial Temperature Distribution Factor (RTDF). Results demonstrate that these parameters primarily govern peak temperature generation in the primary combustion zone and dilution effects within the recirculation zone. Specifically, increasing V_m from 60 to 80 m/s or reducing A_P from 90° to 28° weakens flame coupling, leading to reduced OTDF from 0.227 to 0.153 and peak RTDF value from 0.145 to 0.105. The analysis reveals flame coupling as the dominant factor influencing hot streak generation and migration, outweighing the impact of recirculation zone dilution. Consequently, promoting weaker flame coupling emerges as a key strategy to mitigate radial temperature gradients and enhance combustor exit temperature uniformity. These findings offer valuable insights for optimizing staged combustor designs.