An overview of hot gas ingestion research at the University of Bath

Rim seals are fitted in gas turbines at the periphery of the wheel-space formed between rotor discs and their adjacent casings. These seals reduce the ingestion of hot gases that can cause significant damage to some of the most highly stressed components in the engine. In gas turbine engines this ingestion is principally caused by circumferential pressure asymmetries in the mainstream annulus, radially outward of the rim seal. A superposed sealant flow, bled from the compressor, is used to reduce or, at the limit, prevent ingestion. As the use of this sealing air can reduce the cycle efficiency, it is important to know how much flow is required to prevent ingestion and to understand the associated fluid dynamics and heat transfer when ingestion occurs. This paper presents an overview of experimental results from a research facility which models an axial turbine stage with generic, but engine-representative, rim seals. Measurements of pressure, gas concentration, temperature and swirl are used to assess the performance of different seal designs. As ingestion through the rim seal is a consequence of an unsteady, three-dimensional flow field, the cause-effect relationship between pressure and the sealing effectiveness is complex. The approach at Bath has been to conduct fundamental work to measure and understand the fluid dynamics using generic, fully-instrumented experiments specifically designed for the available measurement techniques. The experimental data is shown to be successfully calculated by simple effectiveness equations developed from a series of theoretical models which can be used to aid the design of more specific engine geometries.