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ALTD Report Summary

Project ID: 296115
Funded under: FP7-JTI
Country: United Kingdom

Final Report Summary - ALTD (Large 3-shaft Demonstrator - Aeroengine intake acoustic liner technology development)

Executive Summary:
The proliferation of air travel and its forecast of an ever increasing global trend brings many benefits in terms of business, trade and leisure for the worlds population, but is not without challenges which need to be overcome to ensure that the local community and greater population can prosper and succeed in the wider context of the advancing travel and transport industry.
A key design driver for the aviation industry is the improvement and refinement of aircraft efficiency and environmental impact which are increasing in importance as the industry grows. More stringent regulations are resulting in the industry developing new technologies and methodologies to ensure that these challenges are overcome. To comply with these requirements airlines and aerospace manufacturers are increasingly targeting noise reduction, weight and production costs to achieve these goals and are key parameters for this project.
Noise generated during aircraft take-off and approach operations is a particular issue for local communities that are in close proximity to airports. In turbofan engines the ducts are lined wherever possible with acoustic panels, for the reduction of radiated noise. The advancement of engine technology has resulted in the noise produced from an engine, and in particular the main fan blades, being significantly different than previous generations of turbofan jet engines.
This has resulted in the need to better study, analyse and evaluate inlet acoustic liners for new and future generation large scale turbofans that will dominate aircraft in the decades to come and ensure that inlet acoustic liners can be adequately designed and optimised to meet current and future aircraft noise regulations.
The main objective of this project is to develop the design and manufacturing capability of advanced acoustic liner and inlet assembly technology in line with the need to achieve environmental and aircraft efficiency targets and provide an opportunity to progress a productionised solution for future applications.

Project Context and Objectives:
The project gave BAB and the project partners UOS and UL to develop technical and manufacturing capability of advanced aero-engine nacelle inlet technology. With key design parameters in mind, Bombardier were tasked with the full mechanical and tooling design, technical development, manufacture and assembly of an advanced and innovative acoustic intake liner for engine testing to Topic Manager requirements. The overall design and manufacturing techniques implemented in the production of the acoustic liner were aimed at validating a TRL [Technology Readiness Level] 6 demonstrator operating under in-flight representative test conditions. The scale and dimensions of the demonstrator allowed BAB to utilise industrial procedures and assembly practices during the design and manufacturing phases and exploited the opportunity to gain knowledge and insight into these productionised techniques for future development outside an R&D environment. In addition BAB was tasked with the integration and assembly of the acoustic liner into a one-piece lipskin/outer skin design which further progressed the manufacturing capability of this novel and unique approach. The emphasis of all the design and manufacturing activities was to identify an array of benefits in terms of the use of advanced materials, production methods, cost control, weight, durability and acoustic performance to progress aero engine intake technology.
The University of Limerick’s (UL) involvement as a primary project participant focused on the testing and evaluation of advanced materials through exposure to environmental factors such as UV, moisture, temperature cycling and airborne particle impingement that would be representative of typical flight conditions. Candidate materials with and without anti-erosion coating systems applied were selected for this study. The effects of this environmental exposure were analysed to determine the effectiveness of the anti-erosion coatings and scrutinised the protection they gave to the underlying material and their suitability for acoustic liner applications.
The University of Southampton (UOS), through their Institute of Sound and Vibration Research faculty, and also a project participant were tasked with assisting in the acoustic definition and optimisation of the acoustic liner parameters in line with the engine noise source to ensure the correct attenuation performance of the deliverable acoustic liner subject for engine testing. UOS were also tasked with interpreting and developing the acoustic results gathered as part of the study into the maturity of laser micro perforation technology. The eventual aim was to attempt to develop a semi-empirical method to more accurately predict the acoustic impedance and attenuation performance of the micro perforation method for acoustic liners.

Project Results:
The key design drivers behind the innovative approach of the design and manufacturing task focused on environmental and sustainability factors including radiated engine noise reduction, manufacturing processes and cost, implementation of novel materials to increase in-service life and improving aerodynamic efficiency to improve aircraft performance. This section will detail the S&T results on each of these design drivers:
• Radiated engine noise reduction;
The primary function of an acoustic liner is to attenuate noise, and on an engine inlet this is particularly important due to the increasing trend of larger fan diameters and shorter engine inlets. The design and manufacture elements of this project focused heavily on increasing the acoustic attenuation performance of the acoustic liner.
Micro perforation technology had only been briefly explored in previous years, so in this project the strategy was to develop the knowledge and understanding of the discipline and increase the manufacturing capability of micro perforate technology through implementation of a productionised approach on a large scale demonstrator. Based on in-house and specialised acoustic testing and resultant post process analysis a robust and reliable predication model for micro perforates was developed. This was significant as this model can now be utilised and implemented for future acoustic inlet designs in the industry to further improve the acoustic attenuation capability of next generation inlets.
The data, methods of analysis and post processing of the results to create this micro perforate model were published and presented at an AIAA conference in front of industry experts by UOS who were leaders in this task.
A study conducted to evaluate the ability to produce the micro perforations in an industrialised environment proved to be highly significant. The study which looked at current laser technology and the quantifying of the recurring costs, cycle time, capital outlay and production capability associated with each system provided significant results and ultimately changed the strategy of the project. The results highlighted the previous misconceptions regarding micro perforation using lasers and concluded that the path to an industrial use for the technology was more complex and challenging than previously understood. Despite this it clarified the current state of the art and realigned the expectations and strategy going forward in this field. The decision to pursue a traditional mechanical perforation approach for the deliverable hardware was directly related to the outcome of this study.
The design of the liner also encompassed concepts which optimise the acoustic attenuation performance of the liner. The location of the honeycomb core was positioned further forward and aft than traditional designs and internal jointing techniques used to secure the cores were greatly reduced in volume and size to gain more acoustic area.
The one-piece or zero-splice technology was also implemented in this project which has been shown through computational and analytical models to provide significant acoustic benefit. Through design concepts and manufacturing trials the zero splice approach allowed BAB to improve processes and tooling strategies to ensure that the productionised solution conformed to the requirements needed to exploit the maximum acoustic benefit.

• Improving manufacturing processes and cost;
The project also presented an opportunity to improve manufacturing costs by utilising novel materials in the acoustic liner construction. The use of advanced adhesives and honeycomb cores provided a level of experimentation to trial the use of these materials in the manufacture of the liner. A tangible outcome of these activities was the adoption of a new adhesive, a better way to manipulate honeycomb cores and improvement on control of pre cured composites during pre-autoclave assembly procedures. The learning gained through these activities were later introduced in production procedures reducing costs and increasing cycle times.
The integration of the acoustic liner to the one-piece lipskin provided major time savings compared to similar production inlet. Preliminary estimates calculate approximately 100 hours of workmanship saving in this type of assembly approach. With potential greater savings in labour hours through further development of the process.
• Implementation of novel materials to increase in-service life;
The project allowed investigation and refinement of current materials used in acoustic liner manufacture. The erosion studies carried out by UL detailed the degradation and comprising of structural integrity due to environmental exposure that would be experienced on in-service acoustic liners. The testing yielded significant outcomes on the material properties. The water impingent tests highlighted the damage that could occur at during certain extreme exposure to precipitation and highlighted the need to consider such circumstances when designing and developing acoustic liners for harsh environments. The UV, moisture ingress and temperature cycling exposure to the materials produced the most interesting results. Accelerated and more representative tests were conducted on a selection of coupons and emphasised the impact of materials with and without the coating systems applied. The overall outcome of the study showed the benefits and limitations of various coating systems and scrutinised the claims of protection of the underlying structural material. The majority of coating systems improve the integrity of the material of which they are protecting but this study showed that they each fail at differing exposure and intensity levels leaving the underlying material vulnerable.
• Improving aerodynamic efficiency and structural weight
The design and the manufacturing concepts implemented in the acoustic liner and the inlet assembly were crucial elements in improving the aerodynamic performance and weight, both of which are increasingly important to the airline industry.
The novel one-piece lipskin/outer skin used during the assembly stage of the project was primarily orientated to a low aerodynamic drag approach. Featuring no split lines, assembly joints or doubler locations the one-piece design provides a greater chance of laminar flow over the lipskin and outer skin surfaces and reducing the occurrence of flow separation under typical flight cases. This reduces the aerodynamic drag penalty associated with current designs and improves aircraft performance and can contribute to a lower fuel consumption level.
The extensive use of composite materials in the acoustic liner provided a significant weight saving when compared to alternative designs. More specific features such as limiting the use of high density honeycomb core in non-critical areas, majority use of carbon fibre facing sheets and back sheets and lowering the footprint of the temperature and pressure probe contributed to this reduction. The one-piece lipskin/outer skin demonstrated even greater weight reduction. Again the extensive use of composite materials showed significant weight benefits. Further development of the design and construction methodologies could yielded even better results.

Potential Impact:
In relation to social implications and socio-economic impact, the ALTD has played a significant role in addressing related European transportation policies and wider environmental issues. The ALTD project has provided significant results and manufacturing capabilities that have directly influenced the requirements needed to meet goals, such as those set out by the ACARE policies, and prove out developing technologies that will support the new generation of aircraft.
More specifically the ALTD project enabled all participants to develop and expand their knowledge through testing, analysis, design and manufacture to accomplish the ever increasing trend of quieter aircraft, more efficient aircraft and higher performance aircraft. The noise reduction concepts utilised in this project have a significant social impact on the future aerospace and airline industries by openly targeting the need for quieter and less acoustically invasive aircraft for communities living, working and socialising around airports and their local vicinities. The need for more efficient aircraft has been addressed in this project through the use of lightweight materials, advanced aerodynamic features for lower drag penalties and better assembly integration techniques, all which have a major influence on the requirement for lower fuel consumption and less emission outputs.
On a wider context, the accomplishments of this project have enabled the European aeronautical industry to maintain a strong position and remain at the cutting edge of aeronautical markets. The exploitations and demonstrating of the technologies and advancements are expected to encourage an expansion of employment opportunities in the European aircraft industries and their associated supply industries, thus generating new markets through the direct development and implementation of technologies exhibited in project.
The results of the project have been disseminated through various channels. The studies on material degradation and environmental exposure conducted by the University of Limerick were published as a dissertation and were distributed by the university in their annual journals. The acoustic optimisation activities, conducted by University of Southampton, culminated with the study relating to the creation of the micro perforation model being presented to peers and industry experts at the 2016 AIAA conference in Lyon, France.

List of Websites:
not public website used for this project.

contact details.
Bombardier Aero structures and Engineering Services, Belfast, BT3 9DZ, United Kingdom

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