The relationship between the plenum to freestream total pressure ratio on film cooling performance is experimentally investigated. Measurements of both the heat transfer coefficient and the adiabatic effectiveness were made on the suction side of the center blade in a linear transonic cascade. Entrance and exit Mach numbers were 0.3 and 1.2 respectively. Reynolds number based on chord and exit conditions is 3 x 10⁶. The blade contour is representative of a typical General Electric first stage, high turning, turbine blade. Tunnel freestream conditions were 10 psig total pressure and approximately 80 °C. A chilled air coolant film was supplied to a generic General Electric leading edge showerhead coolant scheme. Pressure ratios were varied from run to run over the ranges of 1.02 to 1.20. The density ratio was near a value of 2. A method to determine both the heat transfer coefficient and film cooling effectiveness from experimental data is outlined.

Results show that the heat transfer coefficient is independent of the pressure ratio over these ranges of blowing parameters. Also, there is shown to be a weak reduction of film cooling effectiveness with higher pressure ratios. Results are shown for effectiveness and heat transfer coefficient profiles along the blade.