Fully-Cooled Single Stage HP Transonic Turbine: Part I—Influence of Cooling Mass Flow Variations and Inlet Temperature Profiles on Blade Internal and External Aerodynamics

A fully cooled turbine stage is utilized to investigate the combined effects of turbine stage cooling variation and HPT vane inlet temperature profile on the aerodynamics and heat transfer of the turbine stage operating at the proper design corrected conditions. Part I of this paper describes the overall experimental matrix, the influence of the cooling mass flows, and temperature profiles from an aerodynamic perspective. The measurements include internal and external pressures for the blade airfoil. Part II of this paper focuses on the influence of these parameters on the heat transfer to the blade airfoil and the stationary blade shroud. The major results show that cooling levels do not significantly affect the external pressure distributions over the majority of the blade and vane. However, aerodynamic effects of cooling levels and temperature profiles are seen for the vane and blade pressure loading on the suction surfaces. The magnitude of these effects range from 5 to 10% of the local measurement for the reference case, which is the uniform inlet profile with nominal cooling for this study. Inlet temperature profiles and cooling levels have comparable impacts on pressure loading, but their relative influence changes with location, Reynolds number and corrected speed variations have the lowest impact on pressure loading changes, with changes below 5% of the local measurements. Another important result is that unlike un-cooled experiments, the proper normalizing variable for pressures aft of the vane is not the inlet pressure but a “Rotor Reference Pressure”, which adjusts the total inlet pressure by the increase in pressure resulting from the additional cooling mass flows. For the rotor, this consists primarily of the vane trailing edge cooling flows. This simplified model accounts for the effects of the vane cooling, and isolates the changes due to blade cooling. The spread of the cooling flows through the stage is important to the surface heat flux, and has an impact on pressure loadings on the suction surface. The data establishes important guidelines for modelers of cooling flows. The changes observed on the suction side of the airfoils are real, but quite small from an engineering design perspective. Thus the pressure levels are stable and relatively independent of cooling levels, which is critical for good heat-transfer predictions.