Numerical investigation of the aero-thermal performance of a film cooling hole under several modelling assumptions

In gas turbines some parts are exposed to high temperatures from the combustion gases well above the melting threshold of the material. Therefore, advanced cooling techniques are used to protect the parts exposed to these gases. One such system is the film cooling, necessary to guarantee a safe working condition for the turbine high-pressure stages. It consists in the ejection of cold air on the surface of the parts to create an adiabatic layer of gas at lower temperature. A good prediction of the interaction between the mainstream and the coolant jet is important for the design of such advanced cooling system. A numerical study was conducted to investigate the behaviour of film cooling jet for a simple cylindrical hole on a flat plate. The numerical study was devoted to the assessment of different model parameters of the simulation as well as mesh and geometrical features to be able to predict both the aerodynamic and thermal performance of the film cooling by means of a common Reynolds Averaged Navier-Stokes (RANS) approach. A reduced model is studied in a such a way as to give the same aero-thermal conditions that can be seen in a real gas turbine, even though at lower temperature than those in real turbines. Results obtained by means of an experimental setup from the TATEF (Turbine Aero-Thermal External Flow) project are shown along with numerical results obtained from the same working conditions. The blowing ratio effect is studied at three levels M=0.5, M=1.0 and M=1.5, combined with the effect of the turbulence model adopted, standard k-w, SST k-w and standard k-e. Further investigation was conducted in the end to study the effect of the fillet radius both at the channel inlet and outlet sections. In general, the results show the film cooling effectiveness modelled with the SST k-ω to give a better prediction of the results compared to the experiments. Eventually, the steadiness of the simulations does not provide the correct mixing between the mainstream and the coolant jet to match the experiment, therefore conclusions are drawn from the trend of the results that reflect the experiments.