Evaluation of Novel Junction Film Holes for Improving Film Cooling Performance

The junction film cooling has been proposed to deal with the situation of insufficient film cooling performance under limited coolants. Numerical investigations are performed for baseline case and four junction film hole cases (3_junction, 4_junction, 5_junction and 6_junction cases) at the coolant mass flow rate varying from 0.0016 kg/s to 0.0064 kg/s. From the results, due to the expanded film hole exit and the interactions between branch film jets, junction film hole cases can suppress the “injection phenomenon” of film jet and the “entrainment effect” of mainstream, thus to improve film cooling performance, especially the film spanwise coverage. By comparison, under low coolant mass flow rate, the 5_junction case can generate the most obvious film cooling performance improvement. To be specific, at the coolant mass flow rate of 0.0016 kg/s, it achieves 76.92% improvement in area-averaged adiabatic film cooling effectiveness, and at the coolant mass flow rate of 0.0032 kg/s, the improvement is up to 703.85%. Through flow loss analysis, the results show that at low coolant mass flow rate, the junction film hole cases improve film cooling performance and pay a little cost of pressure loss; but under high coolant mass flow rate, they can improve film cooling performance and reduce total pressure loss concurrently. Among them, the 5_junction case generates the lowest total pressure loss coefficient; corresponding to the coolant mass flow rate of 0.0048 kg/s and 0.0064 kg/s, it decreases by 15.90% and 41.58% respectively. Through this study, the junction film cooling for improving cooling performance is provided, which is conducive to further raising turbine intake temperature, thereby improving the kinetic and thermodynamic properties of gas turbines.