Resumen de Heat transfer in cavities adjacent to the main gas path in turbomachinery
This thesis describes the research done during a six year investigation into the heat transfer within cavities adjacent to the main annulus of a gas turbine. The work was started at the Thermal Systems department in Rolls-Royce and continued at the Fluid Mechanics and Aerospace Propulsion Department of the ETSIAE (UPM) under the auspices of the European Union funded programme MAGPI. The principal objective of the study has been to develop and validate computer modelling methods of the cooling flow distribution and heat transfer management, in the environs of multistage turbine disc rims and blade fixings, with a view to maintaining component and subsystem integrity, while achieving optimum engine performance and minimizing emissions. Particular attention has been dedicated to the interaction of the hot main stream gas with the coolant at the rim gaps between rotating and static components as the understanding of this phenomena may lead to significant improvements of SFC. A fully coupled analysis capability has been further developed using combinations of Rolls-Royce in-house and commercially available computational fluid dynamics (CFD) and finite element (FE) thermo-mechanical modelling codes. The main objective of the methodology is to help decide on optimum cooling configurations for disc temperature, stress, and life considerations. The capability also gives us an effective means of validating the method by direct use of disc temperature measurements, where otherwise, additional and difficult to obtain parameters, such as reliable heat flux measurements, would be considered necessary for validation of the use of CFD for convective heat transfer. The high degree of confidence acquired in the CFD tools, as well as the identification of the areas of uncertainty, by means of benchmarking to the temperature measurements, has settled the basis for attempting the resolution of particularly challenging problems focused on the interaction of the hot main stream and the cavity flows.
A two-stage turbine test rig has been developed and improved to provide good quality thermal boundary condition data with which to validate the analysis methods. The modelling methods employed have been compared making use of the experimental data gathered from the rig, running at engine representative conditions. A cooling flow optimization study has also been performed to support a redesign of the turbine stator well cavity to maximize the effectiveness of cooling air supplied to the disc rim region. The benefits of this design change have also been demonstrated on the rig. A brief description of the test rig facility is provided together with some insights into the successful completion of the test program. Comparisons are detailed of disc rim cooling performance for a range of cooling flows and geometry configurations. The new elements of this work are the presentation of additional test data and validation of the automatically coupled analysis method applied to a partially cooled stator well cavity (i.e., including some local gas ingestion with positive net egressed flow) and also the extension of the cavity cooling design optimization study to other new geometries. Furthermore, a study of the flow egressed from an upstream wheelspace into a downstream cavity has been carried out using a variety of methods which includes evaluating the impact of seal clearance.
