Despite the blades downstream of the combustor being cooled in most large gas turbines, the effect this cooling has on their performance is still unclear. Fundamental questions, such as how turbine efficiency should be defined and which flow features reduce performance, remain unanswered. This thesis answers these questions and addresses the problem of how heat transfer affects turbine performance.

Currently, there is a direct contradiction between industrial experience and the academic methods used to evaluate turbine performance. In a cooled turbine, these entropy-centric (exergy) methods predict that the irreversible heat transfer due to cooling would cause an extremely large drop in turbine efficiency (around 4-6%). In practice, this drop is not observed.

By applying a new method called euergy, this thesis demonstrates that the performance of a cooled turbine can be defined in a way that agrees with industrial experience. This method shares the view of the practical device that the ideal work is defined by a reversible adiabatic turbine. A key consequence of this method is the value placed on heat, relative to work, becomes set by the Joule (Brayton) cycle efficiency. This means whenever heat is transferred, or when viscous reheat occurs, the value of this heat should be set by the Joule cycle efficiency.

This new understanding finally allows both the efficiency to be defined and the flow features that change it to be identified. The method also provides cooling designers with a new way of raising turbine efficiency, a form of thermal recuperation in the flow. This mechanism offers the exciting potential that future cooling systems, when added to a blade profile, could reduce profile loss by up to 9%.

Furthermore, the generality of the new method allows all cooled components, however complex, to be systematically analysed for the first time. This is demonstrated using a computational approach. The large-scale effect of heat transfer on performance is captured in newly developed loss models which are then compared with conjugate heat transfer simulations. The small-scale effect of heat transfer on performance is investigated by examining the near-wall region of cooled boundary layers using direct numerical simulation (DNS).

This thesis establishes a new framework and illustrates how heat transfer affects turbine performance. This new understanding allows performance to be communicated across all levels of turbine design. The new method offers the prospect of future innovative cooling schemes which, in addition to cooling the blade, act to raise turbine efficiency.