Rotor cascade assessment at off-design condition: an aerodynamic investigation on platform cooling

Authors

Hamed Abdeh - University of Bergamo, Italy
Giovanna Barigozzi - University of Bergamo, Italy
Nicoletta Franchina - University of Bergamo, Italy

Abstract

The gas turbine is at the centre of the energy transition, but its complex behaviour in off-design conditions is an obstacle to the integration with renewable energy power plants and the formation of a modern hybrid power grid. In the present work, off-design condition has been considered as the ability of the turbine to operate down to 50% to 20% of its nominal intake air flow rate. An important consequence of these off-design points is the change in the inlet incidence angle, which was varied from nominal to -20°. Tests were performed on a seven-blade rotor cascade with platform cooling through an upstream slot simulating the stator to rotor interface gap. To model the impact of rotation on purge flow injection, a set of fins were installed inside the slot, to give the coolant flow a tangential direction. Fins inclination angle was varied according with the different cascade off-design operating conditions tested. The latter covered downstream velocity values up to Ma2is = 0.7 with a fixed inlet turbulence intensity of about Tu1 = 7%. Aerodynamic measurements were performed using a miniaturized 5-hole pressure probe to quantify the cascade aerodynamic loss and secondary flow structures at different experimental conditions. Local LDV measurement were performed in the cascade entrance region, to characterize mainstream and purge flow, and on the blade rear suction side, to monitor the potential for detachment at different incidence angles. A heat transfer measurement campaign (TLC and PSP) was conducted to measure the adiabatic film cooling effectiveness at various coolant to main flow mass flow ratios (MFR %) and different incidence angles. The results describe the complexity of the turbine operating under off-design conditions and critically evaluate the platform cooling to prevent further critical thermal condition inside the hot gas path of the gas turbine.