The principle objective of COJEN is to develop and validate prediction tools that can be used by the aerospace industry to assess and optimise jet-noise reduction techniques. COJEN will deliver the enabling technology to allow European Aerospace industries to:

• design lower-noise aircraft to meet society's needs for more environmentally friendly air transport
• win global leadership for European aeronautics, with a competitive supply chain.

More specifically, COJEN will deliver the methods for designing concepts and technologies for the reduction of aero-engine jet noise, whilst improving industry's ability to competitively develop new products and reduce development time and cost. In order to bring the fundamental work of the FP5 project JEAN (which aimed at prediction of single-stream jet noise) and other programmes to the point where they are useful to industry, the methods developed therein must be extended to cope with hot coaxial jets and arbitrary nozzle geometries. The methods must also be validated to demonstrate their accuracy and reliability. Accordingly, the specific technical objectives of the project are to:

• identify and improve optimal CFD techniques for the prediction of jet flow development from coaxial nozzles of arbitrary geometry
• develop aero-acoustic codes which can predict the acoustic fields from the CFD results
• acquire aerodynamic and acoustic data adequate to validate these codes.

To achieve these objectives, two approaches will be considered. The first is the classical indirect technique in which the turbulent flow field is characterised using a CFD solver and the acoustic modelling uses information extracted from the spatially-resolved turbulence field (local intensity and length scales of the turbulence) to predict the far field noise. The second is the direct computational approach in which Large Eddy Simulation (LES) methods will be used to determine the near field noise.