A numerical study of a high pressure transonic axial turbine stage for heavy-duty applications was performed. Attention was focused on assessing the aerodynamic impact of coolant injection and geometrical features, such as slots, fillets and clearances, on stage performance. First, stator and rotor blade rows were separately studied to single out the main modeling factors. Results showed the way each factor affects the performance of the blade. Influence coefficient evaluation was performed with screening techniques, such as DOE (Design Of Experiments) methods. Physical mechanisms responsible for performance decay were investigated by analyzing the secondary flow structure. After the main modeling factors had been selected and included, a 3D steady analysis of the full-stage configuration was carried out at both design and off-design conditions. Results were also compared with experimental data available from GE-Oil & Gas Nuovo Pignone. The performed analysis showed endwall fillets and coolant injection at the trailing edge slot as the most significant factors for efficiency for both stator and rotor blades. Coolant injection at the showerhead and at the suction and pressure side holes, and the geometrical slot turned out to affect blade-row performance to a smaller extent. Comparison with experimental data showed that a substantial improvement in both stage efficiency and loading factor prediction capability was obtained.

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