EXPERIMENTAL INVESTIGATION OF THE FILM COOLING EFFECTIVENESS DEVIATION USING PRESSURE SENSITIVE PAINT MEASUREMENT FOR DIFFERENT HOLE STRUCTURES

Film cooling is a crucial cooling method to ensure the operation of turbine blades under high-temperature conditions. Turbine blades operate under high-speed and complex flow conditions. In the classic method of measuring adiabatic film cooling effectiveness using Pressure Sensitive Paint, the substitution of the pressure field of the air-case with that of the foreign gas-case has introduced measurement deviation, when the density of two jets is different. The use of a specific ternary oxygen mixture during the test processes enables the correction of the deviation. The shaped holes widely used in turbine blade alter the mainstream-jet mixing process. To obtain the deviation distribution generated during the PSP measurement of shaped holes, measurements were conducted on a flat plate operating at a mainstream Mach number of 0.5 using both the traditional method based on Test3-Air and the corrected method based on Test3-OM for five types of film holes, including a circular hole, a hole with a 45-degree compound angle, double jet ejection, a fan-shaped hole, and a laid-back fan-shaped hole The results reveal that various hole structures broadly exhibit measurement deviation, which generally increases with an increase in the blowing ratio. The deviation originates from the difference in momentum between jets of different densities under the same blowing ratio, leading to distinct flow patterns. Significant negative deviation is observed near the holes under high blowing ratios, while pronounced positive deviation occurs downstream. The distributions of deviation are varied for different structures. The compound angle leads to increased and asymmetrical deviation. For the same pressure deviation, the effectiveness deviation is larger where the film cooling effectiveness is lower. Due to the higher effectiveness downstream of the double jet ejection deviation, the range of the deviation is limited near the hole. The fan-shaped hole and the laid-back fan-shaped hole prevent coolant jet lift-off from the wall, reducing measurement deviation. However, under high blowing ratio conditions, the measurement deviation remains significant and should not be neglected.