Numerical investigations on hydrogen-enriched fuel–air mixing characteristics in a single micromix nozzle for the gas turbine combustor

Efficient hydrogen-enriched fuel–air mixing in a micromix combustor is a key factor that influences the combustion process, flow dynamics, and NOx formation. This study focuses on a single nozzle within a hydrogen-enriched micromix combustor to identify optimal fuel–air mixing strategies and explore the mixing mechanism. Through detailed numerical investigations of gas flow and geometric parameters by Reynolds-averaged Navier–Stoke and large eddy simulation, the influence on the cold-flow field and mixing performance is analyzed. The results indicate that the momentum ratio significantly affects the initial jet trajectory and vorticity magnitude; an optimal momentum ratio of approximately 30 yielded the best mixing characteristics. Preheating the air to 575 K was observed to increase turbulent viscosity and molecular kinetic energy, thereby promoting more effective momentum and mass diffusion rates. Increasing the number of fuel tubes and reducing the tube diameter expanded the diffusion region, improving hydrogen-enriched fuel–air interaction. In addition, higher mass flow rates resulted in deeper jet penetration, while the jet angle significantly influenced the spatial fuel distribution and vortex structure within the premixing tube. A properly adjusted jet angle of 30° led to the breakdown of large vortices into smaller structures, thereby maximizing the contact surface between hydrogen-enriched fuel and air and, thus, enhancing the mixing characteristics. Overall, the micromix combustor demonstrates strong potential for achieving efficient, small-scale fuel–air mixing, which is essential for clean, low-emission combustion.