Buoyancy-Induced Flow and Heat Transfer inside Compressor Rotors

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The gas turbine represents one of the most highly advanced examples of modern day engineering. With over 100,000 scheduled flights per day globally, there is an ever increasing reliance on jet engines to meet our transportation demands. Increasing fuel costs and demanding environmental legislation have driven jet engine manufacturers to produce increasingly efficient power-plants in order to remain competitive. The Advisory Council for Aerospace Research in Europe (ACARE) have set out the target of a 20% reduction in engine fuel consumption and carbon dioxide (CO2) emissions by 2020, relative to 2000 levels.To increase the power output and efficiency - and consequently to reduce the fuel consumption and CO2 production - of gas turbines, it is necessary to increase the pressure ratio of the compressors. This presents a challenge for designers of aeroengines: the higher the pressure ratio, the smaller the compressor blades become, and the size of the clearance between the blades and casing has an increasing effect on the compressor performance and stability. To calculate (and control) these small clearances for transient and steady conditions, it is necessary to determine the radial growth of the compressor discs. This in turn requires the calculation of the transient temperatures of the discs, which involves the calculation of the buoyancy-induced rotating flow and heat transfer inside the compressor rotors. These flows - which are three-dimensional, unsteady and unstable - are extremely difficult and expensive to compute, even by the biggest computers now available. This presents a challenging problem for engine designers, and the research involves an integrated theoretical, computational and experimental programme to address this problem. This project aims to combine experiment, computation and theory to generate a fundamental understanding of buoyancy-induced rotating flow and to develop CFD codes and a theoretical model for use in the compressor-clearance-control technology of gas turbines. The proposal represents an exciting new collaboration between two of the UK's leading research institutes in this area, both with a proven track record of delivering impact to industry. The complementary experience and expertise of the research teams at Bath and Surrey are perfectly suited for such a collaborative enterprise, and the advice and support from Rolls Royce is vital for its success. Not only would this research seek to understand these complex rotating flows, it would also lead to the development of CFD codes and theoretical models that would be used by the designers of the next generation of aeroengines.