Numerical investigation on film cooling and aerodynamic performance for gas turbine endwalls with upstream vane-type and cascade-type slots

Abstract

To further improve the thermal efficiency of gas turbine, the turbine inlet temperature (TIT) increases up to 2000 K, leading to an extremely high heat load on the first-stage vane. Taking into consideration that there are complex endwall secondary flow and the passage vortices which have significant effect on the flow field and thermal behavior near the endwall, it is essential to study the aero-thermal characteristics of endwall and develop efficient endwall cooling approach. In this work, two novel upstream slot structures, referred to as the vane-type slot and cascade-type slot, are proposed, and a comprehensive numerical analysis is conducted to reveal their mechanism and superiority in improving the film cooling and aerodynamic performance of first-stage vane compared with the conventional slot structure. The results indicate that compared with the conventional rectangular straight slot, the coolant jets from two novel slots have a more significant inhibition effect on the development of the endwall secondary flow due to their lower outflow angle and thus higher momentum in streamwise direction, which contributes to reducing the strength of the endwall secondary flow. This is beneficial to provide a lower cascade aerodynamic loss and a higher film cooling effectiveness of the endwall near the suction side leading edge and the higher film cooling effectiveness along the trajectory of the horseshoe vortex on the more downstream region. Moreover, the vane-type slot provides the largest coolant coverage and cooling effectiveness of endwall and the lowest total pressure loss within slot and cascade aerodynamic loss, followed by the cascade-type slot and conventional slot.