A combined experimental and computational study was conducted to investigate the effect of fuel density variations on mixing from a double annular counter-rotating swirl (DACRS) nozzle operated at atmospheric pressure under non-reacting conditions using either helium (He) or a mixture of He and CO2 as fuel simulants. A small probe traversed through the flow collecting gas samples that were sent to gas analyzers measuring the concentration profiles. The resulting measurements are then used to validate the computational fluid dynamics (CFD) model. A commercial CFD code (CFX 10) with a Reynolds averaged Navier-Stokes (RANS) formulation was used to simulate the experiment. Multiple turbulence closures, such as standard and realizable k-ε and SSG Reynolds stress model were evaluated. Additionally, several geometrical considerations, such as modeling a 72° sector versus a full 360°, were tested. While at high fuel-to-air momentum flux ratios (J) the fuel simulant concentration profiles were outward-peaked, and at low J the profiles were center-peaked. An analysis of the experimental results clearly indicate the momentum flux ratio is the most influential parameter controlling mixing in a DACRS nozzle. The simulations produced quantitative agreement with the experimental measurements using the realizable k-ε turbulence closure and only modeling a 72° sector of the nozzle. The complexity of the studied problem required a considerable refinement of the grid to produce an accurate and grid independent solution. The validated model may now be used to explore the design space for optimization of a nozzle for utilization in a syngas application.

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