Aero-thermal optimization of a gas turbine blade endwall with non-axisymmetric contouring and purge flow

Abstract

With the ever-increasing turbine inlet temperature and blade loadings, the thermal management for the endwall of gas turbines is gaining wide attention. Specifically, the increasing blade loadings intensify the cross flows and the blade-endwall interactions, making the design of turbine endwalls operating in such harsh thermal environments a really challenging problem. To resolve such a problem, we propose a novel non-axisymmetric endwall, which is shaped both near the blade leading edge and between the two adjacent blades. The effectiveness of the proposed non-axisymmetric endwall is well demonstrated on a typical large-turning-angle gas turbine with a purge slot. More specifically, in order to obtain a solution that can achieve a good balance between the gas turbine aerodynamic and thermal performance, we carry out three separate optimizations for the non-axisymmetric endwall. The aerodynamic loss, the film cooling effectiveness and the heat transfer coefficient are taken as the objective functions, respectively, for the optimization process. The optimal solution aiming to minimize the heat transfer coefficient achieves the most desirable performance. This solution substantially reduces both the aerodynamic loss and thermal loads at the turbine endwall, since it is effective to suppress both the horseshoe vortex and the cross flows. Furthermore, through a fundamental flow-thermal analysis of the three optimal solutions, an insight into the effects of non-axisymmetric endwall on gas turbine aero-thermal performance is obtained and guidelines for the aero-thermal design of non-axisymmetric endwalls are provided.