Turbulent Flame Behavior near Blow-Off in Multi-Stage Swirl Combustors: A Hybrid RANS-LES Study

Advances in high-performance computing have expanded the use of computational fluid dynamics (CFD) for reacting-flow analysis; however, simulations involving detailed flame kinetics remain computationally intensive for many practical systems. Efficient modeling approaches are therefore essential for predicting flame behavior in swirl-stabilized combustors. This study examines the influence of main-stage swirl intensity on near-lean blow-off characteristics in a multistage swirl combustor using a hybrid RANS–LES framework. The Stress Blended Eddy Simulation (SBES) model, coupled with a Flamelet Generated Manifold (FGM) combustion formulation, is employed to capture key turbulence–chemistry interactions. Results indicate that reducing swirl intensity suppresses the formation of a swirl-stabilized flame, while excessive swirl negatively affects emission performance. For the baseline (S2) and high-swirl (S3) configurations, flame lift-off height increases by 21.0% and 11.96%, respectively, for every 0.1 reduction in equivalence ratio. The S3 case also demonstrates reduced combustion efficiency, with CO emissions rising by 156.4% relative to S2. Local flame extinction is observed in regions of strong droplet–flame interaction, highlighting enhanced quenching susceptibility under near-blow-off conditions. The present study investigates the flame dynamics in a multi-stage swirl combustor using high-fidelity CFD simulations. This study has yet to be validated through experimental analysis and the results presented in this work are entirely computational. Further experimental validation is necessary to verify the results.