Periodic Report Summary 1 - HEXENOR (Development of Helicopter EXhaust Engine NOise Reduction technologies)
Project Context and Objectives:
Despite significant technology improvements over the past twenty years, aircraft noise has become a major problem in Europe, under the pressure of Airport neighbourhood communities and increased awareness of impact of noise on public health1. In 2001, the Advisory Council for Aeronautics Research in Europe (ACARE) put forward a vision for the European aerospace industry and set some challenging targets for 2020 in terms of noise (50% reduction in perceived noise) and greenhouse gas emission reduction also valid for helicopter transportation.
As engine noise is a main contributor to the whole helicopter exterior noise, and as exhaust noise still needs an increased attenuation, our HEXENOR project focuses on understanding exhaust noise sources. The HEXENOR proposal answers to a call of the SAGE5 project and aims to study, design and manufacture three items for helicopter exhaust engine noise reduction, each made of two innovative concepts, a quiet plug and a quiet diffuser which will be mounted on a turboshaft engine demonstrator to reduce the noise radiated by the exhaust. Installing acoustic liners at the exhaust can lead to significant benefit for reducing noise levels from helicopters. In the framework of HEXENOR it will also be the challenge to find a trade-off between the weight and cost constraints.
As increase of both mass and cost restrains the use of acoustic technologies on the current gas turbines, for HEXENOR developments have to be conducted on two points:
• Characterization of two innovative materials the ferritic and TiAl alloy satisfying specifications in addition to the harsh conditions.
• A new liner concept designed as a cavity made of partitions above a perforated plate optimized to fill the mass and cost constrains with an efficient acoustic attenuation
In order to achieve the objectives defined by the call the consortium consisting of experts from various disciplines and backgrounds had to be established. Fundamental and applied researchers from university and a research center, developers and manufacturers from material and mechanical industry are present in the consortium. UTC, the coordinator of HEXENOR, and the COMOTI research center have experience in raising analytical solutions, numerical simulation and experimental testing, whereas three industrial partners have relevant skills in material, Aperam, Form Tech and Gfe, are already active in the field of acoustics of air transportation.
The Hexenor project started on the 1rst of February 2012 and will be finished on the 31rst of January 2013.
Project Results:
To reach the objective of the project the work is split into two main parts:
An “academic” part which was mainly carried out during this first 15 months period and which is in charge of:
• Defining the characteristics of the liner made of a perforated plate with cavity behind (WP2).
• Studying the characteristics of two materials , the K44X steel and TiAl alloy (WP3).
A design and manufacturing part of the three items on the basis of the specifications deduced from the works done in the first part (WP4 and WP5)
The goal of the WP2’s was to determine the characteristics of the liner (hole diameter, plate thickness and hole ratio, number and height of the cavities) in actual aero-acoustics conditions of the engine but satisfying the weight and cost specifications, UTC has conducted a research including experimental and theoretical developments on the basis of a cylindrical duct section with liner located on the wall.
Experiments were therefore conducted on lined barrels specifically design to measure:
• The liner impedance of samples with an impedance tube in order to determine the suitable impedance model to be used for analytical development
• The scattering matrix [S] of the liner duct section with the DUCAT flow duct facility for higher order mode propagation conditions (ka<6)
• The Transmission Loss (TL) and Global transmission Loss (GTL) without flow and the Attenuation of the muffler for flow conditions (M<0,2) with a flow acoustic intensity probe made of a microphone and a hot wire.
An analytical calculation of [S] was carried out and validated with a FE model:
• to calculate without or with flow the scattering matrix, the TL and GTL of the academic mufflers
• to conduct a parametric study to determine the “best liner configuration”
The WP2 has performed nearly all intended works:
1. All no flow and flow experiments
2. The no flow analytical model
3. Analysis of the no flow situation has been conducted
The main results achieved so far by WP2 are:
• The analytical model of the academic muffler is one of the main results of this project.
• The comparison between no flow theoretical and experimental results on the DUCAT facility has shown a very good agreement validating the analytical development taking into account higher order mode propagation in lined wall duct.
• The main goal of WP2 has been fulfilled as the liner characteristics of the three items have been defined for design in accordance with Turbomeca and other partners after a parametric study based on the no flow analytical calculation with the actual exhaust diffuser conditions.
Only works on the flow analytical model and analysis are still ongoing and will be achieved before the end of June.
The WP3 was in charge of studying if the two materials which the items will be made of, the K44X steel and the TiAl alloy are able to satisfy the hard specifications of the engine. Also a special work was conducted on the TiAl alloy to evaluate the sheet manufacturing technology and also to test its formability checking the material’s hot forming property with suitable parameters.
Main works achieved: All metallurgical, thermo-mechanical and fatigue tests on K44X steel and TiAl materials have been conducted. Also Gfe has carried out manufacturing technology evaluation of the TiAl alloy.
The main results are that K44X steel is satisfying the TM specifications. Concerning the TiAl alloy, A4 sheets of TiAl have been rolled with a 0.8mm thickness which also is satisfying the TM specifications. .
Only works concerned with forming the TiAl sheets are still ongoing and will start after the summer holidays.
The WP4 in charge of the design starts month 11 on the 1rst of January 2013.
In accordance between all partners and TM it was decided that:
• The intermediate and long items will be made of steel
• The shorter item will be composed of a perforated plate made of TiAl alloy sheets assembled by a riveting process and steel for the other parts.
A first version of the TiAl nozzle design has been released, as a CAD model in December, 2012, for TM design validation. The validation of the design solution is still pending. The delay in the design phase was mainly due to outstanding issues related to thermal dilatation stresses. Several design solutions have been proposed. The CFD simulations in WP4 have been cancelled, in agreement with TM, to be replaced by existing measured data, but a structural and vibration analysis of the selected design solution will still be required.
The WP5 work did not yet start. Procedures for material supply will be started within June, 2013.
Concluding remarks:
As both academic parts have now been achieved leading to the definition of the liner (characteristics and materials) and as only TiAl forming will start soon, we hope that the project goals will be fulfilled before the end of January 2014.
Potential Impact:
It stated that aeronautics and air transport are to be considered as a strategic economic and social domain to ensure the future of European integration, independence, prosperity, and competitiveness in the global economy.
The European Air Transport sector made up of civil Aeronautics and Air Transport generates a turnover in excess of Euro 94 billion and represents a pinnacle of manufacturing which employs almost half a million highly skilled people directly and spinning-out technology to other sectors. About 2.6 million indirect jobs can be attributed to air transport related activities and a contribution of around Euro 240 billion to gross domestic product. The direct contribution of aeronautics to economic prosperity is a measure of its success in pioneering the “knowledge society” that the European Union is now urgently seeking to achieve in the framework of its Lisbon Strategy for Innovation and Growth. For the Commissioner Busquin there are two great prizes to be gained: global leadership in the marketplace and a world class air transport system for Europe. Whereas a generation ago, “Higher, Further, Faster” were the imperatives for any vision of the future for air transport, now they are “More Affordable, Safer, Cleaner and Quieter”, reflecting the need to combine cost-effectiveness with an uncompromising attachment to safety and environmental objectives.
Despite significant technology improvements over the past twenty years, aircraft noise has become a major problem in Europe, under the pressure of Airport neighbourhood communities and increased awareness of impact of noise on public health. - Exposure to noise constitutes a health risk.
The HEXENOR proposal which aim it is to reduce the noise radiated by the exhaust of the helicopter engine without increasing the cost and the weight is obviously a contribution to the objectives defined in ACARE which has very recently published the report “AERONAUTICS AND AIR TRANSPORT: BEYOND VISION 2020 (TOWARDS 2050)” (http://www.acare4europe.org/docs/Towards2050.pdf).
Therefore the material choices are fundamental:
Ferritic Stainless steel as a low cost material compared to usual special alloys. This material is currently not used in Aeronautics but on the other hand AM get long experiences in the high temperature applications of such ferritic stainless steel, especially for exhaust systems where temperature up to 1000°C in cyclic conditions are reached. We selected the most promising grade, recently developed and patented K44X that passed first validation lab tests at Turbomeca. The project will determine if this transfer of technology from the automotive industry is feasible and is a good opportunity for AM to better understand requirement of aeronautical market.
- TiAl alloy is the weight saving alternative as a light alternative for only one exemplar of Quiet Exhaust diffuser. TiAl is a light material with 3,8g/cm3 outstanding thermal resistance capability. However, it is difficult to form and the room temperature ductility is low as ~2%. Furthermore welding of TiAl sheets is not trivial. Previous envisaged aeronautical applications of TiAl have failed due to other alloy composition and even worse ambient temperature properties as the chosen alloy for HEXENOR. Due to the low stress level of the quiet plug and exhaust diffuser, this application is ideal to demonstrate all the potential for mass gain associated with TiAl alloys.
In addition, some spin-off of the academic work developed on the liner concept in Hexenor to other industries is foreseen, since fluid machines as pumps, fans and internal combustion engines are major noise sources in modern society:
- The air ventilation industry where lining in ventilation channels has to be optimized
- The automotive industry for optimizing exhaust ducts
- The fan and turbine industries
List of Websites:
http://hexenor.utc.fr