Coupled heat transfer analysis of internal and film cooling of turbine blade under medium temperature conditions

Increasing turbine inlet gas temperature is a main approach to meet the demands for high efficiency and thrust of advanced gas turbine engines. Both of internal and film cooling are often used at the same time for the turbine blade's cooling to enhance the overall cooling performance and ensure the blade temperature below to the heat resistance temperature of blade material. Most of open studies focused on the individual cooling effect of either internal cooling or film cooling under normal temperature conditions. However, the actual working conditions of blade cooling is that internal cooling and film cooling affect each other because of the coolant flow through film hole and the heat conduction inside the blade solid regions (including the internal disturbing elements). In addition, the temperature difference between turbine inlet gas and coolant is much high. It is found that there are few studies on the coupled heat transfer characteristics of turbine blade cooling. To establish a numerical method for coupled heat transfer analysis of the turbine blade cooling, the coupled heat transfer in two perpendicular channels which are connected by a dividing wall and a film hole through the dividing wall is numerically investigated by simultaneously solving the air flow and convective heat transfer equations in the two passages. The heat conduction through the dividing wall (including the ribs equipped in the internal channel) and the flow through the film hole are also taken into consideration. The interaction between internal and film cooling can thus be explored. The mainstream inlet temperature is set to be 709 K to consider a medium temperature condition of turbine blade, and Reynolds number is 1.08 x 105. The large-eddy simulation (LES) and SST kappa-omega are employed to verify the applicability of turbulence models for the simultaneous simulation of internal and film cooling by comparing the numerical consequence with experiment from the published literature. It is indicated that LES can capture the fine structure of the flow field and has high accuracy in predicting the cooling effect. It is discovered that the heat conduction through the dividing wall of the two channels increases both of the internal convective cooling and the film cooling of the mainstream channel in comparison to the adiabatic cooling effect without considering the heat conduction inside the solid regions. In addition, the outflow through the film hole improves Nusselt number of internal channel, and the ribs bring about a slight increase of overall cooling effectiveness near the behind zone of the film hole, but decrease in the downstream a little far from the film hole. Besides, adjusting the blowing ratio could achieve higher blade cooling performance. It is suggested that we should not stay in the stage of studying internal or film cooling separately, but carry out more coupled heat transfer analysis of turbine blade cooling to find the appropriate geometric parameter/configuration of internal and film cooling for the fine design of gas turbine blade cooling, especially today when large-scale numerical calculation has become a reality.