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Aggressive Intermediate Duct Aerodynamics for Competitive and Environmentally Friendly Jet Engines


In multi-spool jet engines, the low-pressure (LP) system has a much lower rotational speed and larger radius than the high-pressure (HP) core system. Hence, intermediate S-shaped transition ducts are needed to connect the high-radius LP system with the low-radius HP system. These annular ducts often carry loads, support bearings and have thick structural struts passing through them, making them large, heavy and expensive structures of considerable complexity. In modern aircraft engine design, there is a constant pressure to decrease weight and noise, and increase both performance and time-to-market. Transition-ducts that are more aggressive have become a key to meet these demands on future engines.

Project objectives

The AIDA project will strengthen the competitiveness of the European aero-engine manufacturers and decrease environmental impact through the achievement of the technical objectives, which are given below:

  • improved understanding of the flow physics in aggressive intermediate ducts
  • system integration – knowledge of how aggressive ducts interact with neighbouring components
  • development and tests of a new class of very aggressive intermediate ducts
  • assessment of new advanced vane-duct integration concepts
  • establishment of validated analysis methods and ‘CFD Best Practice Guidelines’ for duct flows
  • tests and modelling of novel passive separation control devices for super-aggressive ducts
  • development of new numerical optimisation techniques for intermediate ducts
  • establishment of design rules and a validation database for aggressive intermediate ducts.

The quantitative project targets are 20% shorter ducts, or 20% increase in duct radial offset or 20% increase in duct diffusion rate. Duct design lead-time and risk for late and serious duct-related component integration problems will also be reduced by 50%.

Description of the work

All the European aero-engine manufacturers, three leading research institutes and five highly reputed universities have concerted their efforts to reach beyond the state-of-the-art in intermediate duct design. The project’s team of 18 experts are dedicating their time to achieving these objectives over four years.

The project is structured into one managerial and six technical Work Packages:

  • Fundamental Investigation of Aggressive Compressor Ducts
  • Fundamental Investigation of Transition Ducts for Turbines
  • New Concepts and Integrated Compressor Duct Design
  • Passive Flow Control and Shape Optimisation
  • CFD Analysis of Aggressive Transition Ducts
  • Data Integration and New Design Rules.

The test facilities that will be mobilised by the AIDA project include some of the best experimental centres of excellence of Europe. One single-spool and one two-spool low-speed compressor facility will be supported by one high-speed compressor rig to carry out eight different measurement campaigns to push the design limits for ducts, with or without struts or swirl. The interturbine duct design space will be improved by resorting to five experiments in one low-speed and one high-speed turbine facility. The design space will be further improved by making use of two complementing measurement campaigns to assess the optimal passive control devices for intermediate ducts. Duct shape optimisation and computational predictions will be used to support experiments by providing pre- and post-test flow predictions, for instance, or by optimising the duct geometries even further.

Expected results

The exploitation of the project’s technical achievements will strengthen competitiveness and decrease environmental risk due to the impact on overall engine characteristics, enabling a 1-2% reduction in engine weight and length, 0.5% and 1.5 % increase in compressor and turbine efficiency respectively, 5% reduction in engine development costs and 10% reduction of engine time-to-market. These improvements will also have an impact on aircraft systems, leading to a 2% reduction in fuel burn and CO2 emissions, 2.5% better operating margin for long-haul aircraft, and will act as an enabler for new classes of low-noise engines.