Effect of Flow Parameter Variations on Full Coverage Film-Cooling Effectiveness for a Gas Turbine Blade

Abstract

The effect of film-cooling holes placed along the span of a fully cooled high pressure turbine blade in a stationary, linear cascade on film-cooling effectiveness is studied using the pressure sensitive paint technique. The effect of showerhead injection at the leading edge and the presence of compound angled, diffusing holes on the pressure and suction sides are also examined. Six rows of compound angled shaped film-cooling holes are provided on the pressure side while four such rows are provided on the suction side of the blade. The holes have a laidback and fan-shaped diffusing cross-section. Another three rows of cylindrical holes are drilled at a typical angle on the leading edge to capture the effect of showerhead film coolant injection. The film-cooling hole arrangement simulates a typical film cooled blade design used in Stage 1 rotor blades for gas turbines used for power generation. An optimal target blowing ratio is defined for each film hole row, and tests are performed for 100%, 150%, and 200% of this target value. Tests are performed for inlet Mach numbers of 0.36 and 0.45 with corresponding exit Mach numbers of 0.51 and 0.68, respectively. The flow remains subsonic in the throat region for both Mach numbers. The corresponding freestream Reynolds numbers, based on the axial chord length and the exit velocity, are 1.3×106 and 1.74×106, respectively. Freestream turbulence intensity level at the cascade inlet is 6%. The results show that varying blowing ratios can have a significant impact on film-cooling effectiveness distribution. Large spanwise variations in effectiveness distributions are also observed. Similar distributions were observed for both Mach numbers.