Unsteady phenomena and realistic geometry effects at the combustor-turbine interface of a large gas turbine

Gas turbines in combined cycle are the cleanest and most efficient form of large-scale thermal power generation, and their use is expected to increase in the future. The most arduous conditions within a turbine are faced by the first stage nozzle guide vanes (NGV). These are located immediately after the combustion chamber and face the highest thermal loads, as well a a complex flow field influenced by combustor conditions. For this thesis, experiments and computational methods are developed and used together to investigate steady and unsteady heat transfer and aerodynamics in the nozzle guide vanes It is beneficial to reduce the heat transfer to components in order to increase efficiency and maximise component life. Improvements were developed to experimental methods which could be carried out in a scale experimental rig, which operated at realistic Reynolds number and Mach number. Thin film gauges were developed for heat transfer measurements at higher sensitivity and spatial resolution than has been possible in the past. The use of a large numbers of unsteady pressure sensors has been pioneered successfully. Improved experimental techniques are applied to optimising heat transfer and aerodynamics resulting from realistic features which are often overlooked in simplified studies. Several combustor chamber geometries are compared, finding that a combustor design that minimised length scales of turbulence structures reduces NGV heat transfer coefficients significantly. This shows the benefits which can be achieved by designing combustor and turbine together in a holistic manner. The unsteady effects of large-scale flow structures generated in the combustion chamber were observed in detail by high resolution unsteady measurements and LES. Instantaneous flow phenomena which occur are measured experimentally, and are explained physically with the support of LES. Instantaneous heat transfer events are found to be sufficient to cause potentially damaging temperature fluctuations to thermal barrier coatings, despite being disguised in time-averaged measurements. The impact of the mid-passage gap between vane platforms on heat transfer and aerodynamic efficiency is measured. An analytical model is developed, which can be used to assess the importance of such gaps in the general case. It is found that great improvements are possible if gap sizes are reduced below a critical threshold. The optimum distribution of cooling flows required to prevent ingress can be calculated by means of a one-dimensional equation, with no need for iterative optimisation. Ingress into circumferential gaps is also investigated, and found to cause damaging local heat transfer. A measurement campaign investigating surface texturing effects on heat transfer is also presented.