University of Bath

Modelling of ingress in an aero-engine gas turbine stage

This programme will provide insight into the thermal effect of ingress in gas turbines and inform the design of cooling systems for SAFRAN Aero Engines.

Our single-stage gas turbine test facility investigates hot gas ingestion in wheelspace cavities.
Our single-stage gas turbine test facility investigates hot gas ingestion in wheelspace cavities.

The gas turbine engine is an adaptable source of power. It's used for applications ranging from the generation of electric power and jet propulsion to the supply of compressed air and heat. Industrial competition and environmental legislation have put pressure on engine manufacturers to produce cleaner and more efficient products.

Efficiency is the most important factor in governing engine performance and life-cycle operating costs. High cycle efficiency depends on a high turbine entry temperature and an appropriately high pressure ratio across the compressor.

The life of turbine components (vanes, blades and discs) at these hot temperatures is limited. This is primarily due to creep, oxidation or thermal fatigue. The turbine can only operate using these elevated mainstream gas temperatures because its components are protected by a relatively cool air from the compressor. But, this cooling comes at a cost. As much as 15 to 25% of the compressor air bypasses combustion to provide the required coolant to the combustor and turbine stages.

Ingress is one of the most important cooling-air problems facing engine designers. Considerable international research effort has been devoted to finding acceptable design criteria. Ingress occurs when hot gas from the mainstream gas path is ingested into the wheel-space between the turbine disc and its adjacent casing. Rim seals are fitted at the periphery of the system. A sealing flow of coolant is used to reduce or prevent ingress. But too much sealing air reduces the engine efficiency. And too little can cause serious overheating and damage the turbine rim and blade roots.

One-stage turbine test facility

We have redesigned the single-stage test facility to incorporate an aero-engine wheel-space geometry. The annular single-stage turbine creates an unsteady circumferential distribution of pressure. This in turn creates the ingestion of hot air in the wheel-spaces. The rim-seals are modular, allowing us investigate state-of-the-art geometries experimentally.