The Influences of Off-Design Incidence Angle and Discrete Hole Shapes on Film Cooling Effectiveness
Detailed tests have been conducted in the cascade heat transfer wind tunnel in order to investigate film cooling effectiveness of single and double-row discrete holes on the leading edge of the pressure surface of a turbine blade. Mass transfer analogy has been used in this experiment. Carbon dioxide was added to the cooling air. The concentration distribution of the carbon dioxide downstream of the cooling film was measured by chromatograph. Two sets of testing blades with discrete holes of different shapes were used. The first set had round holes with diameter of 1.5 mm, and the ejection angle was 70°. The second set had rectangular holes with width of 1.0 mm and whose ratio of length to width was 5, the ejection angle being 90°. The holes between rows were arranged in staggered pattern. It was found that the incidence angle has strong influence on film cooling of turbine blades. The film cooling effectiveness near the ejection hole on the pressure surface (concave surface) is higher than that on a flat plate and on a suction surface (convex surface). Over a wide range of blowing ratio M, the film cooling effectiveness of rectangular hole is much higher than round holes.