Film-cooling effectiveness on squealer cavity and rim walls of gas-turbine blade tip
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Effects of shaped holes on the tip pressure side, coolant jet impingement on the pressure side squealer rim from tip holes, and varying blowing ratios for a squealer blade tip were examined on film-cooling effectiveness. The film-cooling effectiveness distributions were measured on the blade tip, near tip pressure side, and the inner pressure side rim wall using pressure-sensitive-paint technique. Air and nitrogen gas were used as the film-cooling gases, and the oxygen concentration distribution for each case was measured. The film-cooling effectiveness information was obtained from the difference of the oxygen concentration between air and nitrogen gas cases by applying the mass-transfer analogy. The internal coolant-supply passages of the squealer tipped blade were modeled similar to those in the GE-E3 rotor blade with two separate serpentine loops supplying coolant to the film-cooling holes. A row of compound angled cylindrical film-cooling holes was arranged along the camber line on the tip and another row of compound angled shaped film-cooling holes was arranged along the span of the pressure side just below the tip. The average blowing ratio of the cooling gas was controlled to be 0.5, 1.0, and 2.0. Tests were conducted in a five-bladed linear cascade in a blowdown facility with a tip gap clearance of 1.5%. The freestream Reynolds number, based on the axial chord length and the exit velocity, was 1.48 106, and the inlet and the exit Mach number were 0.23 and 0.65, respectively. Turbulence intensity level at the cascade inlet was 9.7%. Numerical predictions were also performed using Fluent to simulate the experiment at the same inlet flow conditions. Predictions for film cooling are presented. Results show a good correlation between experimental and predicted data. The shape and location of the film-cooling holes along with varying blowing ratios can have significant effects on film-cooling performance. Copyright 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
