Abstract
In the first part of the paper, CFD analysis of the combusting flow within a high-swirl lean premixed gas turbine combustor and over the 1st row nozzle guide vanes is presented. In this analysis, the focus of the investigation is the fluid dynamics at the combustor/turbine interface and its impact on the turbine. The predictions show the existence of a highly-rotating vortex core in the combustor, which is in strong interaction with the turbine nozzle guide vanes. This has been observed to be in agreement with the temperature indicated by thermal paint observations. The results suggest that swirling flow vortex core transition phenomena play a very important role in gas turbine combustors with modern lean-premixed dry low emissions technology. As the predictability of vortex core transition phenomena has not yet sufficiently been investigated, a fundamental validation study has been initiated, with the aim of validating the predictive capability of currently-available modelling procedures for turbulent swirling flows near the sub/supercritical vortex core transition. In the second part of the paper, results are presented, which analyse such transitional turbulent swirling flows in a laboratory water test rig. It has been observed that turbulent swirling flows of interest are dominated by low-frequency transient motion of coherent structures, which can not be adequately simulated within the framework of steady-state RANS turbulence modelling approaches. It has been found that useful results can be obtained only by modelling strategies, which resolve the three-dimensional, transient motion of coherent structures, and do not assume a scalar turbulent viscosity at all scales. These models include RSM based URANS procedures as well as LES. To exploit the full potential of LES, however, additional attention needs to be paid to modelling issues such as achieving the necessary grid resolution as well as providing convenient inlet boundary conditions.
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