Loss Predictions in the High-Pressure Film-Cooled Turbine Vane of the FACTOR Project by Mean of Wall-Modeled Large Eddy Simulation

The use of numerical simulations to design and optimize turbine vane cooling requires precise prediction of the fluid mechanics and film effectiveness. This results in the need to numerically identify and assess the various origins of the losses taking place in such complex systems in engine representative conditions. Large-Eddy Simulation (LES) has shown recently its ability to predict turbomachinery flows in well mastered academic cases such as compressor or turbine cascades. When it comes to industrial representative configurations the geometrical complexities, high Reynold and Mach numbers as well as boundary condition statements lead to an important increase of CPU cost of the simulations. To evaluate the capacity of LES to predict film cooling effectiveness as well as to investigate the loss generation mechanisms in a turbine vane in engine representative conditions, a wall-modeled LES of the FACTOR film-cooled nozzle is performed. Composed of a combustor simulator and a high-pressure turbine stage, the test rig of European FACTOR project has been setup to investigate combustion chamber and turbine interaction. The inlet conditions of the turbine stage feature a hot spot representative of modern engine in terms of swirl and temperature gradients. 

A wall-modeled LES of a periodic sector including 2 vanes with their cooling system is performed. A steady inflow featuring a hot spot clocked with one vane obtained by a LES of the combustor simulator is injected at the inlet of the computational domain. After the comparison of integrated values to validate the operating point of the vanes, the mean flow structure is investigated. Due to the clocking with the hot spot, a nozzle experiences a hotter environment than the other one, the hot region migrating preferentially around it. In the coolant film, a strong turbulent mixing process between coolant and hot flows is observed. As a result, the spatial distribution of time-averaged vane surface temperature is highly heterogeneous. Footprints of coolant jets as well as hotter regions from the interaction of the hot spot with the surface are clearly visible. Comparisons with experiment show that the LES prediction fairly reproduces the spatial distribution of the adiabatic film effectiveness. The loss generation in the configuration is then investigated. To do so, the two methodologies, i.e, performing balance of total pressure in the vanes wakes as mainly used in the literature and Second Law Analysis (SLA) are evaluated. The first methodology (balance of total pressure) only highlights the losses generated by the wakes and secondary flows. The contribution of the thermal effect being omitted in the balance. As a result, such a methodology is not fully appropriated for complex film-cooled configuration. To overcome this limitation, the SLA is adopted by investigating loss maps. Mixing losses dominate in the coolant while aerodynamic losses dominate in the coolant pipe region. Advanced analysis of the loss maps confirms that the turbulent contribution to the losses dominate the mean one in the coolant film as well as in the coolant pipes. Although the predictions of the losses generated in the boundary layers is limited by the use of a wall model, the results show that the SLA is an appropriated methodology to evaluate and quantify the loss generation in industrial representative configurations of cooled vanes.