Numerical Analysis of Flow Microstructure Around Cooling Jets in an Annular Combustor: Effects of Kerosene Droplet Size on Mixing, Emissions, Temperature Variance, and Pattern Factor

Abstract Gas dynamics and flow microstructure around liner primary cooling jets in an annular combustor are investigated to quantify how kerosene droplet size governs mixing, NOx, CO formation, temperature, and its variance. A periodic 20-degree annular combustor sector is simulated using CFD RANS modeling with a combination of finite rate chemistry and the eddy-dissipation model for combustion, participating radiation P1 model, thermal, and prompt NOx formation. Four cases with hollow cone sprays with Sauter mean diameters from 15 to 45 μm are assessed with the Rosin–Rammler droplet distribution. The diagnostics further include droplet-cluster trajectories, liner temperatures, and outlet combustion and emission characteristics. The results obtained without incorporating a secondary droplet breakup model show that smaller droplets (15–25 μm) evaporate within or just downstream of the primary zone, producing a compact hot core, thin jet-film layers, higher thermal NOx, and low CO localized to primary-jet shear. Larger droplets (35–45 μm) preferentially migrate toward the liners and reach the dilution row, forming near-wall vapor clusters colocated with elevated temperature variance and CO in jet/film shear layers, while suppressing NOx through cooling and reduced high-temperature residence. At the outlet, an intermediate droplet size yields the most uniform temperature field, whereas the largest droplets produce the strongest hot-cold contrast. These findings clarify the coupling between spray preparation, jet-in-cross flow gas dynamics and provide guidance on selecting droplet size and dilution jet momentum to balance NOx and CO emissions and exit temperature uniformity when secondary breakup model integration is neglected. With the integration of the secondary breakup model of kerosene droplets, the obtained results show that larger droplets (60–80 μm) improve outlet temperature uniformity at the expense of higher CO and NO emissions, whereas smaller droplets (25–45 μm) reduce emissions with slightly increased temperature nonuniformity, demonstrating that secondary breakup governs the interplay between emission formation and thermal quality in liquid kerosene combustion.