Effects of upstream slot geometry on the endwall aerothermal performance of a gas turbine blade under different ejection angle conditions

In the current study, effects of upstream slot geometry with different ejection angles on endwall flow and heat transfer characteristics of a gas turbine blade are numerically investigated. Based on validation of the numerical method, the Reynolds-averaged Navier-Stokes (RANS) equations combined with the standard k-ω turbulence model are adopted in this study. The effects of convergent and divergent slot geometries on near-endwall flow structure and endwall heat transfer behavior are studied when ejection angles are 45 deg and 90 deg respectively. The results indicate that compared with a normal slot, the convergent slot significantly improves the endwall cooling performance when the ejection angle is 45 deg, so the thermal loads on the endwall are remarkably reduced. Moreover, the convergent slot can also decrease the aerodynamic losses in blade passage when the coolant to main flow mass flow ratio is higher than 1.0%. However, when the ejection angle is 90 deg, the advantage of the convergent slot in endwall cooling does not exist and heat transfer on the fore part of the endwall is increased by the convergent slot. Consequently the thermal loads on the fore part of the endwall are enhanced, especially, when mass flow ratio reaches 1.5%, the thermal loads on the endwall near the leading edge are increased by 28% compared with that for the normal slot. Besides, the convergent slot also increases the aerodynamic losses when the ejection angle is 90 deg. As to the divergent slot, it has an adverse effect on cooling protection for the endwall with both ejection angles and its effects on both cooling protection and aerodynamic performance are much less than those for the convergent slot.