Numerical investigation into fuel–air mixing characteristics and cold flow field of single hydrogen-rich Micromix nozzle

• The mixing characteristics and flow field of a novel Micromix nozzle are studied. • Fuel and air are premixed uniformly inside circular and elliptical micro-mixing tube. • Vortex has stronger ability to wrap in the external fluid in vertical jet direction. • Fuel hole shape has obvious impact on fuel spatial distribution and vortex structure. • The merging point and combined point of multiple elliptical jets move downstream. As a promising gas turbine combustor for hydrogen-rich syngas, Micromix combustor may produce new design criteria due to its novel structure. Therefore, the mixing characteristics and flow field of single Micromix nozzle with multiple micro-mixing tubes were studied numerically. The results showed that, the Large-Eddy simulation model was more accurate in cold-state prediction of Micromix combustor than the Reynolds averaged equations model. For mixing characteristics, mass diffusion had greater effect on mixing process of hydrogen-rich syngas than momentum-driven diffusion. With the increase of premixing distance, the effect of fuel–air momentum ratio gradually disappeared. And the difference in mixing characteristics was mainly caused by the shear-layer instability at the initial stage of jet. By reducing the jet-direction diameter of micro-mixing tubes, the mixing uniformity improved, indicating that the jet-direction mixing ability was weak, but there was an upper limit of the mixing uniformity. In addition, fuel hole shapes had obvious effect on vortex structure and vorticity, but little impact on mixing characteristics. For the cold flow field, there was a recirculation region between jets near the nozzle outlet, which was helpful for flame stabilization. Compared with the multiple circular jets, the axial scale of recirculation region formed by multiple elliptical jets was larger, the jet merging point and the combined point moved to the burner outlet.