This paper describes the investigation of the flow characteristics of two double radial inflow swirlers configured for use in a gas turbine combustor. The only difference between the two swirlers is in the contra- and co-rotating flow of air in the inner nozzle arrangement. The isothermal vortex flow field created by the double swirlers has been examined using numerical Model 1. The model also includes a cylinder reaction zone downstream of the swirler. The comparison of flow characteristics is carried out by examination of the spatial resolution of three mean velocity components. The contra- and co-rotating configurations show some discrepancy in terms of total loss factor and mass split ratio between the two swirlers. The comparison of flow fields also indicate that there is almost no remaining swirl further downstream in the contra-rotating configuration, while a significant amount of remaining swirl exists for the co-rotating option. The development of Model 1 to include a typical dilution zone and transition duct leads to numerical Model 2, which was used to investigate the impact on downstream mixing with the dilution air and the emerging temperature distribution at the transition duct exit. Comparing the temperature field for both configurations, the dilution effectiveness increases significantly with dilution jet penetration depth and reduces with spread along the circumferential direction. These effects lead to the central hot core persisting along the transition duct to the combustor outlet for the co-rotating option due to the combination of initial cross flow and a strong swirl, resulting in a considerable difference in the predicted outlet temperature distribution factors (OTDF) of 10.8% and 17.7% for the contra- and co-rotating arrangements, respectively.
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