This was an EU FP6 project with the overall goal of increasing knowledge about noise generation and noise reduction mechanisms as well as validating noise prediction tools for coaxial jets. The project built to a large extent on the previous FP5 project 'JEAN' (Jet Exhaust Aerodynamics and Noise).
Despite the progress in the development of CFD solvers, most of the noise prediction methods currently in use in the aerospace industry were correlations based on empirical databases. These were of very limited practical use for assessing the impact of novel noise reduction techniques on aircraft noise. A more explicit approach was required in which changes to the flow would be explicitly predicted and properly linked to the production of noise.
Significant advances have recently been made towards developing aeroacoustic methods which use CFD results as the input for prediction of the acoustic fields generated by exhaust flows. In Europe, much of this progress was initially made within the 5th Framework project 'JEAN', and some good progress has also been made in national programmes. However, these projects have concentrated mainly on fairly fundamental or limited cases. The industrial requirement is to predict the noise from complex geometries such as coaxial jets with pylons, and from noise reduction devices such as forced mixers and serrated nozzles.
The principle objective of CoJeN was therefore:
- to develop and validate prediction tools which can be used by the aerospace industry to assess and optimise jet-noise reduction techniques.
In order to bring the methods developed in JEAN and the national programmes to the point where they are useful to industry, the methods had to be extended to cope with hot coaxial jets and arbitrary nozzle geometries. The methods also had to be validated to demonstrate their accuracy and reliability.
Accordingly, the specific technical objectives of the project were:
- to identify and improve optimal CFD techniques for the prediction of jet flow development from coaxial nozzles of arbitrary geometry
- to develop aeroacoustic codes which can predict the acoustic fields from the CFD results
- to acquire aerodynamic and acoustic data with which to validate these codes
In CoJeN, CFD techniques for the prediction of the turbulence characteristics of coaxial jets were developed and validated. These were linked to noise source generation and propagation models for the prediction of the near- and far-field noise. The results from these were critically evaluated against data, which was be obtained from a series of carefully designed experiments.
The project was divided into the following steps:
- Project management, specifications and assessment
- Flow prediction
- Acoustic source generation & propagation modelling
- Acquisition of validation data
that included these tasks:
- project management, specifications and assessment;
- flow prediction;
- Reynolds Averaged Navier-Stokes (RANS) techniques;
- Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) techniques;
- Vortex methods;
- technology transfer;
- acoustic source generation and propagation modelling;
- acoustic analogies;
- direct methods;
- hybrid methods;
- acquisition of validation data;
- advanced measurement techniques;
- single and multi-point flow measurements;
- whole field flow measurements;
- acoustic measurements;
- testing and data reduction.
Identification and improvement of optimal CFD techniques for the prediction of jet flow development from coaxial nozzles of arbitrary geometry:
A number of different CFD techniques have been investigated and developed, and their use and limitations with respect to jet aerodynamics and noise prediction is now much better understood. Expertise in the use of these techniques has been transferred to the industrial partners.
Development of aeroacoustic codes which can predict the acoustic fields from the CFD results:
Improved acoustic analogy methods, validated direct methods, (LES, DES) and Hybrid methods have been developed.The partners now have access to a range of methodologies to suit particular applications. Some possible alternative approaches have also been investigated and excluded as unsuitable.
Acquisition of aerodynamic and acoustic data with which to validate these codes:
An extensive test campaign has been successfully completed, using novel and advanced measurement and processing techniques to extract maximum value.
A large database is now available to support further development and validation. This data will continue to be processed and used beyond the end of the project.