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

Off-design condition of a rotor blade cascade with and without platform cooling has been experimentally investigated. The ability of the gas turbine to operate down to 50% to 20% of its nominal intake air flow rate has an important consequence in the change in the inlet incidence angle, which was varied from nominal to -20°. Platform cooling through an upstream slot simulating the stator to rotor interface gap was considered. The impact of rotation on purge flow injection was simulated installing fins inside of the slot, to give the coolant flow a tangential direction. Aerodynamic measurements to quantify the cascade aerodynamic loss and secondary flow structures were performed at Ma2is = 0.55, varying the coolant to main flow mass flow ratios (MFR %) and the incidence angle. The results show that losses strongly increase with MFR. A negative incidence allows a reduction of the overall loss even when coolant is injected with a high MFR. The greater the loss reduction the more negative the incidence.