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 the liner's 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 RANS CFD with finite-rate chemistry/eddy-dissipation combustion, P1 radiation, and thermal and prompt NOx models. Four hollow cone spray cases (SMD 15-45 µm) with Rosin-Rammler distribution are analyzed, including droplet trajectories, liner temperatures, and outlet characteristics. Without secondary breakup, smaller droplets (15-25 µm) evaporate within or just downstream of the primary zone, forming a compact hot core, thin jet-film layers, higher NOx, and low CO. Larger droplets (35-45 µm) migrate toward liners and reach the dilution zone, forming near-wall vapor clusters associated with higher temperature variance and CO, while reducing NOx due to cooling and shorter high-temperature residence. At the outlet, intermediate droplet sizes yield the most uniform temperature, while the largest produce the strongest gradients. With secondary breakup, larger droplets (60-80 µm) improve temperature uniformity but increase CO and NO, whereas smaller droplets (25-45 µm) reduce emissions with slightly higher non-uniformity, indicating the role of breakup in emission-thermal quality.