ANALYSIS OF COMBUSTOR-TURBINE INTERACTION BY USING COUPLED AND DECOUPLED SCALE-RESOLVING SIMULATIONS UNDER REPRESENTATIVE OPERATING CONDITIONS

The physical phenomena due to the interaction between the combustor chamber and the first stage nozzle arouse an ever-increasing interest. In fact, a complex and unsteady flow field, characterized by a high level of turbulence and temperature distortions, usually can be found at the interface plane between the two hot gas path components, especially with the implementation of lean-burn combustors that allow the reduction of NOx emissions, but at the cost of requiring highly swirled and turbulent flows to stabilize the flame. Such severe conditions at the inlet of the first stage nozzle can have a potential impact on the performance of the component, resulting in a perturbation of the heat transfer, the aerodynamics and the effectiveness of the cooling system. To highlight the risks and uncertainties associated with carrying out decoupled simulations, scale-resolving simulations have been carried out to guarantee an accurate resolution of most of the flow structures while keeping the computational cost low. Firstly, a fully integrated combustor-nozzle setup, including a realistic turbine nozzle cooling system has been investigated under realistic operating conditions. The results have then been compared with those coming from a SBES decoupled simulation of the first stage nozzle alone. In this case, the prescribed time-varying inlet boundary conditions have been extracted from a SBES of the stand-alone combustor where the nozzle has been replaced with a discharge convergent that preserves the Mach number of the NGV while guaranteeing the same throat area. Moreover, in order to assess the discrepancies between different CFD approaches, the results coming from the correspondent preliminary RANS S1N simulation are here also included, by imposing as inlet boundary conditions two-dimensional maps from the time-averaged solution of the precursor SBES of the stand-alone combustor. Thus, the present work concentrates on the comparison and the analysis of numerical SBES simulations of an integrated combustor-NGV configuration and isolated NGV RANS and SBES simulations to assess the impact of the presence of the combustor under realistic operating conditions and realistic annular geometry.