Impacts of gas-turbine combustors outlet flow on the aero-thermal performance of film-cooled first stage nozzles

Modern aero-engine and industrial gas turbines typically employ lean-type combustors, which are capable of limiting pollutant emissions thanks to premixed flames, while sustaining high turbine inlet temperatures that increase the single-cycle thermal efficiency. In such technology gas-turbine first stage nozzles are characterised by a highly-swirled and temperature-distorted inlet flow field. However, due to several sources of uncertainty during the design phase, wide safety margins are commonly adopted, which can have a direct impact on the engine performance and efficiency. Therefore, with the aim of increasing the knowledge on combustor-turbine interaction and improving standard design practices, two non-reactive test rigs were assembled at the University of Florence, Italy. The rigs, both accommodating three lean-premix swirlers within a combustion chamber and a first stage film-cooled nozzles cascade, were operated in similitude conditions to mimic an aero-engine and an industrial gas turbine arrangements. The rigs were designed to reproduce the real engine periodic flow field on the central sector, allowing also to perform measurements far enough from the lateral walls. The periodicity condition was enforced by the installation of circular ducts at the injectors outlet section as to preserve the non-reactive swirling flow down to the nozzles inlet plane. For the aero-engine simulator rig and as part of two previous PhD works, of which the present is a continuation, an extensive test campaign was conducted. The flow field within the combustion chamber was investigated via particle-image velocimetry (PIV) and the combustor-turbine interface section was experimentally characterised in terms of velocity, pressure and turbulence fields by means of a five-hole pressure plus thermocouple probe and hot-wire anemometers, mounted on an automatic traverse system. To study the evolution of the combustor outlet flow through the nozzles and its interaction with the film-cooling flow, such measurements have been also replicated slightly downstream of the airfoils' trailing edge. Lastly, the film-cooling adiabatic effectiveness distribution over the airfoils was evaluated via coolant concentration measurements based on pressure sensitive paints (PSP) application. As far as the industrial turbine rig is concerned, the same type of measurements were carried out except for PIV. Within such experimental scenario, the core of the present work is related to numerical analyses. In fact, since the design of industrial high-pressure turbines historically relies on 1D, circumferentially-averaged profiles of pressure, velocity and temperature at the combustor/turbine interface in conjunction with Reynolds-averaged Navier-Stokes (RANS) models, this thesis describes how measurements can be leveraged to improve numerical modelling procedures. Within such context, hybrid scale resolving techniques, such as Scale-Adaptive Simulation (SAS), can suit the purpose, whilst containing computational costs, as also shown in the literature. Furthermore, the investigation of the two components within the same integrated simulation enables the transport of unsteady fluctuations from the combustor down to the first stage nozzles, which can make the difference in the presence of film cooling.