SILENCE(R) is the largest European Commission research project dedicated to aircraft noise reduction, a major cause of concern around European airports. The project is focussed on the development of aircraft noise reduction technologies, and its main objectives were the validation of individual technologies and a cost/benefit analysis of technological applications across the product range.
The project addresses the issue of aircraft noise through three major objectives:
- Large scale validation of noise reduction technologies whose development was initiated by EU and national projects in '98.
- Assessment of the applicability of these technologies to current and future European products with minimum cost, weight or performance penalty.
- Determination of the associated achievable noise reduction, novel concepts to be validated include low-noise fans, combustors and LP turbines, scared intakes, novel intake, bypass and hot-stream liners, nozzle jet noise suppressors, active control techniques and airframe noise reduction technologies.
Unless this technology can be developed and validated to reduce aircraft noise, traffic is likely to be limited by noise restrictions, affecting indirectly general economic growth.
The project is focussed on the development of aircraft noise reduction technologies, and the task involved the validation of individual technologies and a cost/benefit analysis of technological applications across the product range. Research spanned several main areas, including engine and airframe source noise, nachelle technologies and active control.
Combined with innovative low noise operational procedures studied at the same time, SILENCE(R) has achieved a 5 dB noise reduction. This marks the medium term objective of the European Commission's PCRD R&D Framework Programs, and marks a significant advance towards ACARE's (EC's Advisory Council for Aeronautics Research in Europe) research goal of a 10 dB reduction in aircraft noise by 2020.
SILENCE(R) has met the goal of validating large scale noise reduction solutions concerning the engine (aeroacoustic design, active technologies), nacelle (aeroacoustic design, innovative acoustic treatment, active noise control) and airframe (aeroacoustic design).
SILENCE(R) carried out tests of more than 35 prototypes to check 10 noise reduction technology concepts. These included several advanced low noise fan rotors, as well as components for a complete low noice nacelle (negatively scarfed intake, 'squid' nozzle fitted with high frequency liner), flight tested on an Airbus A320. Flight tests were also carried out on the Airbus A340 with landing gear fitted with aerodynamic fairings.
More than 35 prototypes were tested as part of the project, along with studies of improved operational procedures to reduce aircraft noise.
- Engine source noise: The research on engine source noise spanned the fan, compressor, turbine and jet noise. A low noise compressor was designed using CFD by modifying the inlet guide vanes and the first stator of an existing large scale compressor model. With the new design, the sound power level of the first rotor blade passing frequency tone was significantly reduced under the appropriate operating conditions. Futhermore, this reduction was achieved without compromising the aerodynamic and mechanical characteristics of the compressor. Low noise fan designs were developed for both high bypass ratio (HBR) and ultra high bypass ratio (UHBR) engine concepts, by capitalising on computational aeroacoustic multidisciplinary design optimisation techniques. An advanced design for the HBR engine has already undergone large scale tests at the AneCom Aerotest Facility. Researchers also tested the acoustic and aerodynamic performance of alternative exhaust nozzle shapes designed to reduce jet noise, using Onera and QinetiQ facilities, as well as an Airbus A320 flying testbec.
Nacelle technologies: Research focussed on both the nacelle geometry and acoustic liners. One design possibility for a low noise nacelle was a negatively scarfed inlet (NSI), a concept that is intended to change the directional pattern of the radiated engine noise, so that more noise will be directed upward, and less noise downward. After extensive wind tunnel testing on scale models at Onera, flight tests were made with an NSI mounted on one of the engines of an Airbus A320 at Moron (Spain) and Tarbes (France). The noise benefit of extending the acoustic liner over the intake lip was demonstrated on a static test of a Rolls Royce Trent prototype and in flight on the A320. Research on nacelle acoustic liners included the development and assessment of zero splice inlet liners. Since conventional liners are manufactured in several pieces (typically three), splices are necessary to join the pieces together. It is well known that these splices have a negative effect on the performance of the liners. This is not only because of the reduced area covered by the lining material, but also because the splices cause the prevailing circumferential acoustic modes to shatter to other modes, which are less effectively attenuated. Large scale research on
The important factors tomanage the project were:
- Solid background through previous European Commission projects
- Matrix management structure with effective risk management
- In-depth technology evaluation, to support the cost benefit analysis of different options.