Bath turbine team plans "world first"

Working with funding from the EPSRC and Siemens, engineers at the the facility are currently focusing their efforts on improving the design of gas turbine secondary air systems.

One of the most important cooling-air problems facing gas turbine designers today is the ingestion of hot mainstream gases into wheel spaces between the turbine discs and their adjacent casings. Rim seals are fitted at the periphery of the system, and a sealing flow of coolant is used to reduce or prevent ingress.

However, too much sealing air reduces the engine efficiency - with an associated increase in fuel consumption and CO2 emissions - and too little can cause serious overheating. This results in damage to the turbine rim, blade roots and disc, so getting the correct sealing balance is therefore of critical importance.

Previous research carried out at the University successfully modelled ingestion into a single-stage gas turbine. That research had great industry success in improving the design of gas turbine rim seals through extensive experimental measurements made on the stationary turbine disc and in the wheel-space between the discs.

The group is now about to begin work on a new heat transfer programme, which according to the project’s leader Dr Carl Sangan, will build on its earlier work in the area.

‘New infrared technology developed here at Bath will be used in conjunction with new specifically developed analysis techniques to obtain crucially important rotor metal temperatures at engine operation conditions for use by the designer,’ said Sangan.

‘This will be a world first - many researchers have measured the minimum coolant flow rate necessary to prevent ingress using measurements on the stator, but no one has simultaneously measured the heat transfer from the gas to the rotating turbine disc after the gas has entered the wheel-space.’

The team is also about to begin construction of a completely new test facility - based on a Siemens industrial power turbine - that will simulate the internal workings of real engine and allow the team to carry out detailed experiments of its performance and cooling systems.