The Effects of Vane Showerhead Injection Angle and Film Compound Angle on Nozzle Endwall Cooling (Phantom Cooling)

The effects of airfoil showerhead injection angle and film cooling hole compound angle on nozzle endwall cooling (second order film cooling effects, also called “phantom cooling”) was experimentally investigated in a scaled linear cascade. The test cascade was built based on a typical industrial gas turbine nozzle vane. Endwall surface phantom cooling film effectiveness measurements were made using a computerized pressure sensitive paint (PSP) technique. Nitrogen gas was used to simulate cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness can be obtained by the mass transfer analogy. Two separate nozzle test models were fabricated, which have the same number and size of film cooling holes but different configurations. One had a showerhead angle of 45° and no compound angles on the pressure and suction side film holes. The other had a 30° showerhead angle and 30° compound angles on the pressure and suction side film cooling holes. Nitrogen gas (cooling air) was fed through nozzle vanes, and measurements were conducted on the endwall surface between the two airfoils where no direct film cooling was applied. Six cooling mass flow ratios (MFRs, blowing ratios) were studied, and local (phantom) film effectiveness distributions were measured. Film effectiveness distributions were pitchwise averaged for comparison. Phantom cooling on the endwall by the suction side film injections was found to be insignificant, but the pressure side airfoil film injections noticeably helped the endwall cooling (phantom cooling) and was a strong function of the MFR. It was concluded that reducing the showerhead angle and introducing a compound angle on the pressure side injections would enhance the endwall surface phantom cooling, particularly for a higher MFR.