The effect of rail crown film hole injection angle and blowing ratio on the flow and cooling performance of the squealer tip in a turbine blade

Squealer tip is considered as an efficient and reliable tip geometry design in leakage loss control and thermal load reduction in heavy-duty gas turbine blade. The cooling and aerodynamic characteristics of a squealer tip with different film hole parameters are investigated after validating the numerical approach. Firstly, superior aerodynamic and cooling performance of the rail crown film hole (RCFH) scheme is proved by comparing three squealer tip structures. Subsequently, two kinds of injection angles (streamwise injection alpha and normal injection fi) and three angle values (35 degrees, 90 degrees, and 145 degrees) are studied in RCFH schemes. Finally, a compound angle scheme consisting of optimal alpha and fi is investigated at blowing ratios (M) varying from 0.5 to 2.0. In varied alpha hole schemes, the velocity of the coolant can be divided into the radial and streamwise components, the effects of which on leakage control are complementary, leading to minimal sensitivity of total leakage flow rate (LFR) to alpha. Increasing and decreasing alpha can both enhance the coolant attachment on the rail crown surface compared with the radial injected scheme. In varied fi hole schemes, more coolant momentum is used to resist the leakage flow as fi increases, which results in remarkable LFR reduction. Moreover, the back-press effect of leakage flow on the coolant is markedly enhanced, improving the utilization of coolant. In compound angle scheme, increasing M leads to enhanced impingement on clearance flow, and the maximum values of average film cooling efficiency (eta) on the rail crown and cavity floor appear at M = 1.0 and M = 1.5, respectively.