High Effectiveness Tip Cooling Using Inclined Slots

Abstract The tip of the high-pressure turbine blade is critical for gas turbine performance. Hot gas leaking through the tip gap tends to oxidize and erode the blade while generating significant aerodynamic loss. Squealer tips are often used to maximize efficiency, but the thin rims are thermally vulnerable and difficult to cool. The resultant degradation often limits engine life, turbine entry temperatures, and thermal efficiency. This work considers means to improve the cooling of squealer tips to minimize degradation. Compared to conventional, cylindrical-hole designs, a step-change improvement in cooling effectiveness can be achieved using near-tip slots. In this configuration, coolant is ejected in an approximately streamwise direction along the pressure side rim, cooling a large area with high effectiveness. Experiments characterizing cooling and aerodynamics are performed in a representative linear cascade on an inclined slot design developed to enhance manufacturability while retaining high cooling effectiveness. This design is shown to more than double the cooling effectiveness on the pressure side rim compared to a conventional discrete-hole baseline. Improved coolant shielding is retained for varying mass flowrates, tip clearances, and density ratios. Aerodynamic measurements show that the slot design can outperform the baseline provided the coolant mass fraction between the slots is suitably optimized.