Aerodynamic Loss Penalty Produced by Film Cooling Transonic Turbine Blades

Aerodynamic loss measurements are presented for a state-of-the-art film cooled transonic gas turbine rotor blade tested in a two-dimensional cascade. A mixture of carbon dioxide and air, which correctly simulated engine coolant-to-mainstream density ratio and blowing rate, was ejected from each of five individual cooling hole rows in the aerofoil suction surface. The temperature of the coolant was equal to the cascade inlet stagnation temperature. The dependence of blade row efficiency and turning on outlet Mach number, blowing rate, and coolant-to-mainstream density ratio was investigated. Measured surface static pressure distributions were compared with time-marching predictions for both the datum aerofoil and film cooled blades. Detailed suction surface boundary layer measurements both upstream and downstream of a cooling film were compared with available differential calculation procedures. Unexpectedly, films downstream of the throat, even at blowing rates near unity, did not generate significantly higher losses compared to prethroat suction surface films on this aerofoil.