Overview
In the aeronautic industry there is currently a critical deficiency in the armoury of tools and methods used to predict and control interior cabin noise; namely the ability tp quickly, accurately and reliably determine the sound power entering the reverberant cabin interior at a large number of locations and over a full range of frequencies. The aircraft industry needs to validate and calibrate prediction models and advanced tools for the cost-effective design of low-noise cabins. The reduction of interior noise in aircraft and helicopter cabins is a critical aspect of maintaining competitiveness of the European Aerospace manufacturing industry. Low cabin noise is crucial for passenger comfort and is a consequential factor in the commercial success of aircraft and helicopter design.
CREDO research supported two top-level objectives identified in the Strategic Research Agenda and the Vision 2020 Report:
- to meet society's needs for more efficient, safer and environmentally friendly transport;
- to win global leadership for European aeronautics, with a competitive supply chain, including small and medium size enterprise.
In particular, the CREDO project aimed to strengthen the competitiveness of the European aerospace industry on the global market through a full co-operation between manufacturers, suppliers, high-tech companies, SMEs, research centres and universities. These were joined together within the consortium, to develop innovative concepts and breakthrough technologies to improve understanding of acoustic problems and increase efficiency in acoustic design of aircraft and helicopter cabins by new coupled experimental and numerical techniques.
The project could be considered as an open upstream research fully coherent with the three objectives of Research Area 1 'Strengthening Competitiveness' of the work programme:
- to reduce aircraft development costs by improving the efficiency (increasing accuracy and reducing development time) of the whole vibro-acoustic design procedure in all its facets;
- to reduce aircraft operating costs through reduction in fuel consumption, owing to the possibility of decreasing the weight of structural components (e.g. using composite materials) but maintaining or improving the acoustic performances at the same cost level; decreasing maintenance costs;
- to increase passenger choice with regard to on-board comfort by offering quieter aircraft and helicopter cabins.
The CREDO project achieved its objective by pursuing two mutually interdependent technical tracks:
- Local measurement and processing algorithms, which require, at most, only local acoustic characteristics for the determination of the entering power. No large scale modelling of the aircraft cabin was required and as such the development was entirely generic and may be applied in any reverberant environment. A local approach was, for example, the determination of the accurate entering acoustic power from a single window in flight.
- Global measurement procedures and associated processing using inverse numerical methods, in which an account of the reflections in the aircraft cabin is made by building a global experimental and numerical model of the whole or a large part of the cabin interior and then inverting from measured sound data to the required entering sound power. In contrast to the local, generic approach, this global approach resulted in models that were specific to a particular cabin application.
The project was divided into seven work packages (WP). The first five WPs focused on research and technological development activities, WP6 was devoted to the synthesis of results and innovation-related activities, and WP7 covered the project management. After a clear definition of industrial specifications and requirements (WP1), the basic idea of the project was to develop innovative experimental and numerical tools and procedures (WP2) for detailed local acoustic imaging of entering acoustic intensity inside aircraft and helicopter cabins, taking into consideration the reverberant nature of these environments.
This approach employed a hitherto unavailable microphone array concept: the double layer array, together with purpose-developed processing and procedural algorithms. The feasibility study was performed using adaptations of 3D beam forming and scanning laser Doppler vibrometry to provide acceptable results in a cabin environment in flight conditions. Specific design of experiment (DoE) procedures for cabin noise measurement, and uncertainty evaluation and inverse methods for test-based model identification for fibrous materials were also developed.
As an interactive and mutual development, these techniques were extended to a global acoustic model of the whole or a large part of the cabin interior and then inverting from measured sound data to the required entering sound power (WP3). This was achieved with pioneering inverse finite element implementat
Funding
Results
CREDO introduced advanced tools for efficient and time-saving flight testing. The quality of the data permitted in-flight research to be performed at the same time, including innovative inverse modelling for data post-processing.
This opens up several important possibilities: direct and efficient evaluation of new configurations, materials and new passive and active solutions; fast trouble shooting in existing aircrafts and helicopters to fix manufacturing errors; acoustic quality control for new aircrafts before delivering to the customer, time and cost reduction in flight tests, etc. The proposed tools are easy to manage, fast and completely non-intrusive.
Similar results have never been obtained with such resolution and furthermore they have never been applied to flight tests before.
The techniques allow the identification of the entering intensity into the cabin independently from the reverberant nature of the environment. Nevertheless further developments are needed for the optimisation of cabin internal surfaces absorption in order to design optimal materials able to absorb the entered noise.
Technical Implications
Innovative Contributions:
- to improve understanding on the noise generation and propagation phenomena;
- to improve the efficiency and reduce time in the whole design procedure;
- to improve accuracy in numerical simulation;
- to improve efficiency, reduce time and costs in all acoustic tests; and
- to have tools to handle noise problems in general with higher performances and lower costs applicable for all the kind of aircraft and helicopter cabins.
Application Areas:
- Aeronautics and Space
- Sound Package Industry
- Transportation sector (automotive vehicles, trains, ships etc.)
- Civil buildings