Improving Turbine Efficiency by Combining the Effects of Rim Seals and End-Wall Contours in the Presence of Purge Flow

Project: Research council

Description

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 new environmental legislation stimulating reduced CO2 emissions. Competition within the industry and the external pressure from government has compelled engine manufacturers to produce ever cleaner and more efficient products. The most important parameter in governing engine performance and life cycle operating costs is the overall cycle efficiency. High efficiency depends on a high turbine inlet temperature and an appropriately high pressure ratio across the compressor. In order to optimise efficiency, modern gas turbines operate at temperatures far beyond the metallurgical limit of the components (vanes, blades, seals and discs). The efficiency is influenced by the internal-air systems which provide cooling and sealing air. Purge (or sealing) flow is used to prevent the ingress of hot, mainstream gas through rim-seal gaps into the wheel-space between the turbine disc (rotor) and its adjacent casing (stator). The mixing between the egress of this purge flow and the mainstream gases alters the behaviour of the secondary flow-field near the hub endwall and results in a deterioration of aerodynamic performance. Designers use non-axisymmetric end-wall contouring (EWC) and leading-edge fillets to influence the static pressure field and guide the secondary end-wall flow to reduce losses. The interaction between the purge and mainstream flows, and its influence on the secondary flow-field, is complex and unsteady; further, designers need to ensure that any improvements resulting from EWC do not detrimentally affect the performance of the rim seal or compromise the mechanical integrity of turbine components. Industry is moving towards a combined design of the rim-seal geometry, seal-clearance profile and mainstream end-wall contours, principally through the use of computational fluid dynamics (CFD). The proposed project will build a new experimental facility specifically designed to investigate the fundamental nature of the egress-mainstream interaction. The facility will feature independently interchangeable components: EWC profiles, blade-fillet geometries, rim-seals and rim-seal exit profiles. The research programme will employ the recently funded Versatile Fluid Measurement System (VFMS), awarded to the University of Bath by the EPSRC Strategic Equipment Panel in 2014. The unique VFMS will provide quantitative flow visualisation, for the first time, tracking the plumes of egress in three dimensions as it passes through the downstream rotor and the unsteady velocity field. Simultaneous measurements of the rim-seal effectiveness will ensure that performance benefits are not achieved at the expense of increased ingress. The data will be used to validate a complementary CFD programme conducted at Siemens, with the aim to gain fundamental insight into the governing fluid-dynamics and to translate new design concepts to the engine. The experimental and computational programmes are symbiotic in nature with academia and industry working together to translate new ideas and understanding into future engines.
StatusActive
Effective start/end date1/10/1531/03/19

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Seals
Turbines
Engines
Secondary flow
Gas turbines
Flow fields
Computational fluid dynamics
Rotors
Turbine components
Wall flow
Industry
Fluids
Geometry
Compressed air
Flow visualization
Air
Fluid dynamics
Gases
Operating costs
Propulsion