Investigation on unsteady formation and evolution of high-temperature zone in a staged swirl combustor

Abstract

The high-temperature zone of a laboratory staged swirl gas turbine combustor was studied under different Stratification Ratios (SR) based on experimentally validated Large Eddy Simulation (LES). CH4/air mixtures were adopted with a constant global equivalence ratio of 0.5. Three flame conditions with SR = 1, 2 and 3 were chosen for Particle Image Velocimetry (PIV) and OH Planar Laser-Induced Fluorescence (OH-PLIF) measurements. The LES was performed with the Flamelet-Generated Manifold (FGM) combustion model and validated against the experimental velocity fields and flame structures. Then, a detailed analysis of the formation, evolution, and dissipation of the high-temperature zone was conducted. It is observed that a larger SR deteriorates the uniformity of the exit temperature distribution. One major reason is that with increased SR, rich-burn region is observed to be more dominant. This leads to enhanced non-premixed combustion and an extended heat release region towards downstream, which intensively contribute to the high-temperature zone formation. Additionally, vortices along the shear layers are found to enhance the mixing between fluids of different temperatures, which plays a crucial role in dissipating the high-temperature zone. Higher SR leads to a larger Primary Recirculation Zone (PRZ), and the partially dissipated high-temperature fluid can be recirculated into the PRZ, thus increasing the dissipation distance. With lower SR, however, the high-temperature parcels can be broken and even completely dissipated. This accounts for lower temperature gradients and a more uniform exit temperature distribution. The findings from this study offer new perspectives on understanding the effect of temperature in the primary combustion zone on the exit temperature distribution.