This paper describes the aero-thermal design and validation of an advanced axial flow turbine. This turbine, which has evolved from the existing and proven GT26/GT24 design consists of an optimised annulus flow path using high lift airfoil profiles and improved aerodynamic matching between the turbine stages. A major design feature of the turbine has been to control and reduce the aerodynamic losses, with particular attention being devoted to minimising the secondary, trailing edge and blade tip losses. The advantages of these design changes to the overall turbine efficiency has been verified by extensive controlled experimentation in high-speed cascade test facilities; by the utilisation of 3D multi-row computational fluid dynamics analysis tools, and via engine tests.
In addition to the aerodynamic design modifications of the turbine, the thermal designs of the turbine vanes, blades and heat-shields were also optimised. For the first stage film cooled vane and blade airfoils and platforms, both the film cooling layout and operating characteristics were improved. And for all the internally cooled airfoils, the internal heat transfer design features were additionally optimised, which allowed for more homogenous metal temperature distributions on the airfoil and endwall surfaces. The verification and validation of the thermal designs of the turbine components was confirmed via extensive dedicated testing in high-speed cascades for the film cooling performances, and in scaled perspex models for the internal heat transfer coefficients and local flow distributions.
The complete turbine was further tested and validated in the GT26 Test Power Plant in Birr, Switzerland via a dedicated turbine thermal paint test run and a subsequent performance and mapping testing phase.