The highly adaptable gas turbine engine is one of the most frequently utilised sources of power in the modern age. Derivatives exist in applications ranging from the generation of electric power and jet propulsion to the supply of compressed air and heat.
The world market today is driven by increasing fuel costs and reducing CO2 emissions brought about from new environmental legislation. Competition within the industry and the external pressure from government has compelled engine manufacturers to produce ever more cleaner and efficient products.
Researchers from our Gas Turbine Research Unit have secured grants and funding from both the Engineering and Physical Sciences Research Council (EPSRC) and from multinational engineering conglomerate Siemens to carry out a number of research programmes predominantly aimed at improving the design of gas turbine secondary air systems.
Leading one of the projects, Dr Carl Sangan from our Department of Mechanical Engineering said: “The new facilities here at Bath will allow us to greatly expand on our existing work, and construct a series of new test rigs to experimentally and theoretically model many different aspects of the complex cooling systems employed in a modern engine.”
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 here at Bath 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 forthcoming research projects being carried out in our new gas turbine laboratory will allow the team to develop their previous achievements by not only transforming the single-stage facility to allow for a new EPSRC funded experimental heat transfer programme, but also in the construction of a completely new test facility.
The new 1.5-stage gas turbine rig will simulate the internal workings of real engine (albeit at benign conditions) and allow the team to carry out detailed experiments of its performance and cooling systems. The new test vehicle is based on a Siemens industrial power turbine and, like its real life counterpart, will produce power that will be regenerated back to the national grid.
Speaking of the heat transfer programme, Dr Sangan said: “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. 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 UK-based Siemens will receive a competitive advantage, both in exploiting the data generated from the research and also in significantly influencing the 1D design methodology within the company.