Numerical investigation on film cooling performance and heat transfer characteristics of turbine blade squealer tips with ribs above the film holes

The turbine blade tip is subjected to considerable thermal stress as a consequence of the inevitable leakage flow at the tip clearance, leading to elevated temperatures. It remains a great challenge in the field of blade tip cooling design. This work provides a novel rib structure design strategy for enhancing tip cooling and thermal performance. The four squealer tips (Case 1, Case 2, Case 3 and Case 4) combined with ribs situated above the film holes are to be evaluated and compared. A numerical investigation is conducted to analyze the tip film cooling performance, as well as the tip heat transfer characteristics and flow pattern characteristics, with the inclusion of varying ribbed squealer tips. The results indicate that the ribs positioned above the film holes at the leading edge (LE) enhance the tip film cooling effectiveness, whereas the rib suited above the film holes at other part of squealer tip weaken cooling effect. The highest area-averaged film cooling effectiveness is obtained in Case 4 structure, which increases by 29.1 % compared with no rib squealer tip. The heat transfer performance is able to be improved at different ribbed squealer tips. The highest improvement of tip thermal performance occurs at the Case 1 with the ribs positioned above the film holes at the LE. The heat transfer coefficient decreased by 13.2 % in Case 1. Furthermore, the novel ribbed squealer is demonstrated to control the leakage flow and change the aerodynamic losses. The structure of Case 2 and Case 4 with the middle ribs serves to diminish the total pressure loss coefficient. Specifically, as for Case 2 and Case 4 structure, the area-averaged total pressure loss coefficient decreases by 2.1 % and 1.93 % respectively.