Measurement of ingress through gas turbine rim seals

One of the most important problems facing gas turbine designers today is the ingestion of hot mainstream gases into the wheel-space between the turbine disc and its adjacent casing. A rim seal is fitted at the periphery and a superposed sealant flow is used to prevent ingress. The aim of this PhD research was to design a new rotor-stator testing facility, from which both flow physics and future heat transfer characteristics in relation to ingress could be measured and analysed, along with a detailed investigation into the sealing characteristics of turbine rim-seals there from. The rig was constructed as an engine representative model of a gas turbine wheel-space, from which data correlations could tentatively be scaled and applied to actual engine design. The novel testing facility was designed in great detail for both sealing effectiveness research and to investigate the thermal effects of hot gas ingress; insight never previously achieved. An extensive commissioning process was undertaken to ensure that the correct, albeit benign, fluid-dynamic conditions were created inside the single stage turbine rig. Effectiveness data are presented for single-clearance rim-seals in a variety of ingress conditions from which a fundamental understanding is developed for both rotationally-induced and externally-induced ingress. A newly developed orifice model is validated against the experimental data, resulting in theoretical predictions of the sealing effectiveness characteristics of various rim-seals. It is suggested that these predictions could be scaled to engine representative conditions where they could act as a future design tool for secondary air system engineers. The theory is then extended to the application of double clearance-seal configurations, whereby the beneficial aspects are shown both theoretically and experimentally, leading on to the suggestion of a possible optimisation process resulting in an ultimate double seal. It is postulated that this would be the highest performance that can ever be achieved with a double clearance configuration.