Film Cooling Performance Comparison of Blade Tips With a Trailing Edge, Pressure Side Cutback or a Suction Side Squealer in a Transonic Linear Cascade

Abstract

Abstract Film cooling effectiveness and leakage flow play crucial roles in turbine blade heat transfer. In contrast to the conventional trailing edge cutback squealer blade tip (CB-tip), this study aims to compare the film cooling effectiveness of a suction side squealer tip (SS-tip) under different blowing ratios (M = 1.0, 1.5, 2.0) and density ratios (DR = 1.0, 1.5, 2.0). This experiment is conducted in a 3-blade cascade wind tunnel under transonic conditions, with inlet and outlet Mach numbers equal to 0.29 and 0.75, respectively. While applying the Pressure Sensitive Paint (PSP) technique for film cooling effectiveness measurements, both top-view and side-view perspectives were employed to illustrate the distribution of local cooling effectiveness across various regions of the blade. Furthermore, two coolant injection scenarios were investigated: (i) combined tip and pressure side cooling and (ii) pressure side-only cooling. In addition to measuring the surface effectiveness, PSP can also be used to estimate the leakage flow across the blade tip by analyzing the local static pressure distribution. For the CB-tip, the film cooling effectiveness within the cavity increases as both the blowing ratio and density ratio increase. The PSP technique clearly captures the accumulation of coolant within the cavity and the coolant discharge near the trailing edge in the vicinity of the squealer cutback. When the blade tip is outfitted with only a suction side squealer, the film cooling effectiveness on the blade tip is comparable to that of the full squealer with the trailing edge cutback. This similarity is achieved as the CB-tip design requires 14–20% more coolant to achieve the same blowing ratios as the SS-tip. The advantage of the suction side squealer is further demonstrated as leakage flow across the tip is reduced compared to the conventional, full squealer with a trailing edge cutback.