Effect of shelf squealer tip configurations on film cooling effectiveness

Film cooling effectiveness and heat transfer were measured in squealer tip configurations on the blade tip surface. Three different shelf squealer tip geometries were studied: conventional, vertical, and inclined. The experiment was carried out in a wind tunnel with an inlet mainstream Reynolds number, based on the axial chord length of the blade, of 140,000. The experiments were conducted in five blades in linear cascade with an averaged turbulence intensity of 8.5%. The film cooling effectiveness and heat transfer coefficient on the tip surface were obtained using the transient IR thermography technique. For the pressure side film cooling holes, averaging blowing ratios (M) of 1.0 and 2.0 were set. The results showed the film cooling effectiveness distributions on the tip surface. Owing to the mainstream, the cooling effect appeared after x/Cx = 0.15 and the film cooling effectiveness tended to increase toward downstream of the trailing edge. Additionally, the heat transfer distributions were investigated regarding the film cooling holes. In the presence of film cooling holes, the heat transfer distribution had more uniformity than without them on the pressure side. As the blowing ratio increased from 1 to 2, the heat transfer was decreased on the tip surface. The heat transfer ratio represented the change of heat transfer distribution with and without film cooling holes. Those of results were compared in three squealer tip geometries. The overall area-Averaged net heat flux reduction (NHFR) levels on the tip surface were enhanced as the blowing ratio increased. The NHFR of the shelf squealer tip configurations was better than that with the conventional squealer tip.