Numerical Prediction of the Heat Loads on a Non-Reactive Test Rig for Combustor-Turbine Interaction by Using Hybrid RANS-LES Approach

Abstract

Abstract In order to further improve gas turbine efficiency and performance and reduce NOx emissions, the ever-increasing employment of lean-premix combustors results in very severe, complex and unsteady conditions at the inlet of the first stage nozzle, introducing a possible alteration of the aerothermal behavior of the component. This is considered a recurring problem especially during the gas turbine engine design process and, for this reason, in the recent years, it has become an important and discussed topic in the framework of gas turbines design. In the present study, an annular sector rig, made by a non-reactive, trisector combustor simulator and nozzle cascade, where both adiabatic effectiveness and HTC measurements had been carried out, is investigated by performing a systematic computational study by using a hybrid RANS-LES approach. Firstly, in accordance with the standard industrial design practice, a periodic configuration of the stand-alone NGV was created in order to evaluate HTC on the vane surface by performing RANS simulations and by using 1D profiles from the experiments as inlet boundary conditions. Then, in order to improve the accuracy and reliability of the prediction of the HTC on the NGV and of the flow field outgoing from the combustor, a fully integrated combustor-stator periodic domain has been investigated by performing a SBES simulation. Moreover, in order to carry out further analyses on the nozzle, in correspondence of the position of the interface plane between the combustor and the stator, a set of unsteady data have been extracted and stored from the fully integrated SBES calculation in order to generate realistic unsteady inlet boundary conditions for the non-cooled NGV configuration. In particular, the NGV has been then studied by carrying out RANS and SBES simulations as well by employing the k-ω SST and Transition SST to model the turbulence effects. Eventually, numerical results have been compared to the experiments in order to evaluate the discrepancies between different CFD approaches. The comparison between numerical predictions and the available experimental results was exploited to assess the capability of advanced scale-resolving methods in the characterization of the mutual combustor-turbine interaction, along with the heat transfer coefficient behavior. This evaluation aims thus to assess if such more advanced and more time-consuming methods, including also turbulence models able to capture the transition, can be more reliably used for a proper prediction of the vane thermal loads.