Effect of Suction Side Squealer Tip Height on Blade Tip Film Cooling in a Transonic Cascade

Several studies have identified that using a suction side squealer on the blade tip is beneficial for reducing leakage flow, while achieving comparable film cooling effectiveness to a full squealer. The suction side squealer increases the local pressure on the tip, and leakage through the gap is reduced. This study investigates the effect of squealer height on tip leakage flow and film cooling effectiveness. At a given tip gap (1.6% of the 138 mm blade height), two different heights (1.84% and 3.68%) of a suction side squealer were tested with various coolant mass flow rates (MFR = 0.08%, 0.12%, and 0.16%) and density ratios (DR = 1.0, 1.5, and 2.0). The experiment was conducted in a 3-blade cascade wind tunnel under transonic conditions, controlling the outlet Mach number to 0.75. Pressure Sensitive Paint (PSP) was applied to the middle test blade to measure the film cooling effectiveness. Additionally, the local static pressure distribution on the tip surface, measured by the PSP, was used to estimate the tip leakage flow. The test results distinctly present the difference in the tip surface static pressure, resulting in variations in tip leakage flow for the two configurations of the suction side squealer. Moreover, compared to the previous study, the current configuration also demonstrates the positive effect of cooling hole location on the film cooling effectiveness on the tip surface.