Conditioning of Leakage Flows in Gas Turbine Rotor-Stator Cavities

Hot gas ingress can occur in gas turbines, where mainstream fluid enters the cavity formed between the turbine disc (rotor) and its adjacent casing (stator). A rim seal is fitted at the periphery of the discs and a superposed sealant flow – typically fed through the bore of the stator - is used to reduce, or in the limit prevent, ingress. Parasitic leakage flows pass through pathways created between mating interfaces of engine components. Owing to the aggressive thermal and centrifugal loading experienced by turbines during the operating cycle, the magnitude of these leakage paths are difficult to predict. The engine designer must consider – and typically estimate – the effect of leakage on hot gas ingestion.

This paper considers the potential for leakage flows to be conditioned in order to minimise their parasitic effect on cooling, and ultimately engine, performance. Measurements of ingestion in a 1-stage gas turbine rig employ CO₂ gas concentration, static pressure and total pressure to examine the rotor-stator flow structure. Data is presented for a range of sealing and leakage flow combinations, during which the effect of co-swirling and counter-swirling the leakage flow is investigated. Co-swirl is found to improve the sealing effectiveness by up to 15% compared to the axially-introduced baseline and counter-swirled configurations.

Varying the momentum of the leakage flow was considered by passing consistent mass-flows through a range of inlet areas. Increasing the momentum was seen to cause a more pronounced inflexion in the sealing effectiveness relationship with superposed flow-rate. The onset of this inflexion was seen to correlate linearly with a non-dimensional momentum coefficient.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .