Clean Sky Project

The ‘Clean Sky Joint Technology Initiative’ with an estimated budget of 1.6 billion euros represents the largest European aeronautical research project so far. This ambitious program is equally funded by the European Commission and the aviation industry, running from 2008 to 2017. It aims to develop new technologies into working technology demonstrators that can significantly reduce the ecological footprint caused by the aviation industry in terms of fuel burn and noise emissions.

Despite such high levels of competition among the companies involved in Clean Sky, ARA has enjoyed a high level of success. We have led or contributed to seven successful bids, accounting for more than 10% of the UK’s share. Up to Call 11 (January 2012), ARA has won 8 bids, 6 of which it is coordinating. With 20 submitted proposals this translates into a long term success of 40%. These projects represent a combined total budget of 3.7 million euros and are described below.

CallProject SynonymConsortiumKeywords
1stADOCHAARA, ISVRComputational
1stIDOHAPARAInnovative Hub Design
1stVELOCIRAPTORManchester Univerity, ARAActive Flow Control
3rdCARDARA, VZLU, Glasgow UniversityHelicopter hub drag
5thLOSPAARA, FAMAero-acoustics
5thDEAFCONARAActive control
7thCLARETLiverpool University,
ARA, Stirling Dynamics
Load control and
11thENITEPARA, FFTAero-acoustics


As noise regulations around airports become stricter, fast and reliable tools for the prediction of the noise generated by high-lift systems are increasingly desirable. The aim of the project is to enable routine assessments of the acoustic properties of wings and high-lift systems already at design stage. Supported by the University of Southampton’s Institute of Sound and Vibration (IVSR), ARA has designed and implemented a fully parallelised Boundary Element Method (BEM) that was delivered to the Italian Aerospace Research Centre (CIRA). Based on a statistical acoustic model by Agarwal, it provides broad band noise predictions for 2-dimensional or 3-dimensional geometries based on a given RANS-flow solution.


Innovative Hub Design for CROR-Propeller Rig

Due to the increase in the use of air transport, the European aeronautical industry is now obligated to find more fuel-efficient and innovative approaches in the industry. Counter-Rotating Open Rotors offer the potential of a significant 20% fuel burn reduction compared to classical turbofan engines in service today. In support of a major wind tunnel test by Airbus, ARA delivered two customised hub designs, whose innovative layout allowed quick, accurate and repeatable blade setting changes, minimising test time. This was achieved in close cooperation with the Office National d’Etudes et Recherches Aerospatiales (ONERA) and the Nationaal Luchten Ruimtevaartlaboratorium (NLR), who were responsible for the CROR rig itself and the blade design, respectively.


‘Active flow control’ aims to influence the natural flow around an aerodynamic body by active or energy-consuming methods, such as suction or air being blown through the surface. One of the aims of this project is separation control, ensuring manoeuvrability and minimising the air vehicle’s drag.

The VELOCIRAPTOR module, a synthetic jet actuator delivered by the University of Manchester and ARA provides a single spanwise linear array of 30 synthetic jet actuators. In comparison with the previous prototype, the VELOCIRAPTOR unit’s required part count has been reduced by a third and the lead time for manufacturing reduced by three quarters. The power density of the actuator unit has been increased, with a demonstrated peak velocity of around 90ms-1 at 200V peak-to-peak. The integrated real-time actuator health monitoring system represents another important step towards the applicability of such actuators in aviation. 


The increasing concern about the adverse environmental effects of engine emissions has resulted in the need to identify methods to reduce the fuel burn of helicopters. A major source of aerodynamic drag for helicopters is from the rotor hub, hence the interest in this area. Thus, significant fuel burn reductions are envisioned via drag reductions obtained by a new generation of suitable fairings around the part of the hub exposed to the airstream.

 The experimental CARD research program, undertaken by ARA, the University of Glasgow and VZLU (the Aerospace Centre of the Czech Republic), aims at accurate qualitative measurements of the effectiveness of different fairings by designing, manufacturing and testing a customised helicopter model with a powered rotor. Its significant size (a quarter-scale Dauphin about 3m long) will enable accurate, three-dimensional flow visualisation to identify the vortex systems responsible for the rotor hub drag.


Despite the recent major advances in the reduction of aircraft engine noise, there is still a great concern about the effects of this noise on the local environment during take-off and landing. One potential method of further reducing these effects is using innovative horizontal tailplane designs as a noise shield for engines mounted on the rear fuselage.

ARA will lead a program of work to design and manufacture an innovative wind tunnel model to enable the acquisition of aerodynamic and acoustic data. Nacelles and pylons will be included to accommodate two turbofan simulators which are to be supplied by DNW or ONERA. A set of high aspect ratio wings will be produced, incorporating removable leading edges and trailing edge flaps. This will allow a wide range of configurations to be investigated, including clean, take-off, landing, airbrakes on/off. A modular empennage will also be produced to investigate the potential for reductions in acoustic noise. These items will be designed to interface with the remainder of the model which will be provided by a partner who is independent of this work program.

The resultant model will be tested in the DNW LLF low-speed wind tunnel in the Netherlands, allowing investigation into the effectiveness of the empennage in shielding engine noise and the aerodynamic efficiency of the wing, relating to low-speed take-off, landing performance and handling qualities. A large number of steady and unsteady pressure sensors will be installed in the model. Kulites will be mounted in the thin nacelle and empennage, supplemented by strain gauges mounted on the empennage to measure loads.


The DEAFCON project aims to investigate the use of smart high lift devices to be deployed on the next generation of both short and long-range aircraft. A large scale half model for testing in a low speed pressurised wind tunnel is to be designed  (manufacture will be addressed in a subsequent Call for Proposals). The model wing will be designed to achieve Natural Laminar Flow at cruise conditions, with an innovative high lift system (to be supplied as an output from an earlier Clean Sky Call). The model will utilise a new Krueger flap, smart flaps and both single- and double-slotted flaps, a removable leading edge section, spoilers, airbrakes and ailerons. The design work will be undertaken solely by ARA. The new wing and associated hardware will be designed to utilise an existing model fuselage for future low-speed wind tunnel tests.


CLARET is a European Clean Sky project concerned with the control and alleviation of loads for a regional turbofan aircraft, through the use of a morphing winglet. Winglets can provide beneficial effects both in terms of drag reduction and spanwise loading for particular phases of flight, including during gusts.

Through designing a novel adaptive winglet, capable of controlling both cant and twist, it is envisioned that optimum aerodynamic performance will be achievable through the various flight regimes. A CFD based aerodynamic design of the device applied on a baseline Turbo-Fan Aircraft configuration model will be undertaken, followed by a preliminary layout definition of the structure and actuation system required for the device. Detailed parametric studies will then be performed to investigate the performance of the device in terms of both drag and loads alleviation capabilities on its own, and also in combination with conventional and control actuators, and both compared to the baseline configuration. ARA is working with its partners, Bristol University and Stirling Dynamics, in the CLARET consortium to deliver modern technology into the Green Regional Aircraft Programme of Clean Sky.


This project concerns the requirement to perform a combination of experimental wind tunnel tests and numerical simulations, allowing the study of acoustic refraction through the aerodynamic boundary layer over a fuselage. The aim of the research will be to acquire experimental acoustic data to validate and develop numerical simulation methods in order to better understand the complex phenomena of noise transmission from Contra-rotating Open Rotor engines (CROR) into the aircraft cabin at cruise conditions.

ARA will lead this program of work and apply its expertise in wind tunnel testing and model design and manufacture, developing modern techniques, including traversing mechanisms for the hot-wire probes and high-speed acoustic data recording. The tests will be performed in the ARA Transonic Wind Tunnel using an acoustic liner. An existing fuselage model will be utilised, incorporating extensive steady and unsteady pressure sensor installations and a large array of microphones.

The numerical acoustic simulations will be performed by Free Field Technologies (FFT) using CAA (Computational Aero-Acoustics) codes, which will be assessed and developed using the experimental acoustic data from the wind tunnel tests.

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