Film-cooled turbine endwall in a transonic flow field: Part II - Heat transfer and film-cooling effectiveness

Thermodynamic and aerodynamic measurements were carried out in a linear turbine cascade with transonic flow field. Heat transfer and adiabatic film-cooling effectiveness resulting from the interaction of the flow field and the ejected coolant at the endwall were measured and will be discussed in two parts. The investigations were performed in the Windtunnel for Straight Cascades (EGG) at the DLR, Goettingen. The film-cooled NGV endwall was operated at representative dimensionless engine conditions of Mach and Reynolds number Ma(2is) = 1.0 and Re-2 = 850,000 respectively. Part II of the paper discusses the thermodynamic measurements. Detailed temperature measurements were carried out on a turbine stator endwall. In order to determine the surface heat transfer and adiabatic film-cooling effectiveness, an infrared camera system in a rectilinear wind tunnel measured the endwall temperatures in the transonic flow field. The adiabatic film-cooling effectiveness was determined using the superposition method. Measurements were carried out to first, validate the assumptions of theory and second, analyze the error associated with the measurements. Effects of coolant ejection from a slot and three rows of holes were investigated and compared with each other. The influence of Mach number and blowing ratio on the heat transfer were further aspects of the investigation. Strong variations in heat transfer and film-cooling effectiveness due to the interaction of the coolant air and the secondary flow field were found. Based on the results of this investigation an improved cooling design will be investigated in a follow-tip project.