Film-Cooling Effectiveness of Diffusion Slot Hole on Turbine Blade Tip With a Leading Edge Open Squealer

Abstract This paper focuses on the effects of leading edge film holes on the film-cooling effectiveness of the blade tip, using pressure-sensitive paint technique. A leading edge open squealer was introduced to utilize the leading edge coolant. The effectiveness of integrating leading edge, tip, and pressure side film holes was examined. Two film hole geometries, i.e., cylindrical hole and diffusion slot hole, were tested and compared. The experiments were carried out in a low-velocity linear cascade with a mainstream Reynolds number of 430,000, a mainstream turbulence intensity of 3.6%, and a density ratio of 1.5. The results showed that the leading edge film holes affect mainly the front part of the tip cavity, in which the film holes located at the pressure surface side of the stagnation line play a dominant role. Compared with a typical double-sided squealer, the leading edge open squealer significantly improves the film effectiveness of the blade tip, particularly the front part. For various blowing ratios, the relative increase in area-averaged effectiveness is roughly between 11% and 51%. Moreover, the simplified blade tip film hole layout can achieve high film effectiveness in the front and middle parts of the blade tip cavity. The hole geometry has little influence when used at the leading edge; however, the diffusion slot hole has obvious advantages when used at the blade tip cavity and pressure side.