Investigations of improved heat transfer instrumentation for cooled turbine stages

This thesis describes the development of heated double-sided thin film gauge configurations for transient heat transfer measurements. By heating the substrate it is possible to measure the heat flux over a range of wall temperatures, which improves the resulting regression and leads to a more accurate determination of the adiabatic wall temperature and the heat transfer coefficient. The heated gauges can be used to measure the heat transfer of a film-cooled high-pressure turbine stage with engine-realistic combustor exit flows (hot-streaks and swirl) in order to study turbine aero-thermal performance in the presence of cooling flows. This thesis also presents the aerodynamic and heat transfer design as well as the mechanical assessment of the first fully cooled turbine stage for the Oxford Turbine Research Facility (OTRF). The high-pressure turbine stage is designed for lean-burn combustor interaction effects and has engine-state external cooling features. Platinum thin film resistive gauges are the most advanced instrumentation for transient heat transfer measurement where high frequency response is required. Double-sided thin film gauges, consisting of two thin film temperature gauges mounted on either side of an insulating layer, have the advantage that the driving temperature difference is directly determined at the point of interest. A new gauge design is presented, which combines double-sided thin film gauges with the possibility to heat the substrate layer. Two arrangements of heated gauges have been developed, namely double-sided gauges with an underside thin film heater and self-heating double-sided gauges. These gauges yield an improved regression without the need for complex heating systems. The lateral conduction effects have been investigated using analytical models. The performance of different gauge types is quantified based on the quality of the regression. The heated gauge arrangements have been tested in the OTRF under engine-representative conditions on uncooled and cooled MT1 high-pressure nozzle guide vanes. Measurement strategies have been implemented to obtain the time-dependent temperature trace over a range of heating powers and calculate the convective heat transfer. This improved measurement technique allows for an accurate determination of non-dimensional parameters such as the Nusselt number and the film cooling effectiveness.