Film cooling is the main technology adopted to guarantee safe working conditions of vanes and blades of High-Pressure Turbine stages. Recent experimental investigations highlighted that unsteady interaction between the coolant jet and the hot gas contributes to the lateral dispersion of cold flow over the cooled surface. Hence, considering the harsh working environment of these devices, a fair prediction of their thermal performance requires accurate modelling of the interaction between cold and hot gas. In this paper, an experimental setup originally studied at the University of Karlsruhe during the EU funded TATEF project is numerically investigated to determine the influence of high-frequency unsteady fluctuations on the thermal performance of the cooling device. The case study consists of a film cooling hole positioned on a flat plate, working at engine-like conditions. Unsteady Reynolds-Averaged Navier-Stokes equations are solved for a compressible flow in transonic conditions on a hybrid mesh. Turbulence is modelled using the Scale-Adaptive Simulation method, which is enforced to correctly model the interaction between the coolant and the main flow. Scale-Adaptive Simulation has already been used to evaluate the aero-thermal performance of the present case and has demonstrated its ability to solve the turbulent scales that are characteristic of the inertial range. Three different sets of conditions are analyzed by varying the blowing ratio from 0.5 to 1.5, aiming at highlighting the unsteady mechanisms occurring for different penetrations of the coolant into the hot gas. Time-averaged unsteady results are compared with the available experimental data to determine to what extent hybrid modelling allows for correctly predicting film cooling performance at different blowing ratios. Instantaneous solutions are then analyzed to investigate the time-dependent flow field in the vicinity of the jet exit section and on the cooled surface. Eventually, Spectral Proper Orthogonal Decomposition is enforced to identify the principal fluctuation modes associated with the coolant time-dependent penetration into the main flow.
|Acceptance date - 9 Jan 2022