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WindTunnel Tests on an Innovative Regional A/C for Noise assessment

European Union
Complete with results
Geo-spatial type
Total project cost
€997 002
EU Contribution
€747 752
Project Acronym
STRIA Roadmaps
Vehicle design and manufacturing (VDM)
Transport mode
Airborne icon
Transport policies
Societal/Economic issues,
Environmental/Emissions aspects
Transport sectors
Passenger transport,
Freight transport


Call for proposal
Link to CORDIS

WITTINESS addressed the acoustic measurement campaign of a previously (in a different CfP) designed WT-model, equipped with engine-demonstrators. In order to tackle this project a consortium including a company experienced in design, structural mechanics and aerodynamics, a SME, a manufacturer and a university with a strong focus on acoustic measurements proposed an approach to use the previously designed model, introduce necessary design changes, perform the necessary tests and postprocess the results in terms of acoustic behaviour.

The consortium is build up as follows:

  • IBK is a small company coordinating the project and performing design work in the project. IBK is also leading the consortium building the WT in the previous project ESICAPIA.
  • REVOIND is a small Italian company specialised in manufacturing complex parts. Revoind's main task in this project is to manufacture the model.
  • University of Rome, Prof. Camussi, brought acoustic knowledge into the consortium, which is needed for preparing the acoustic tests and post-processing of the acoustic tests.

The project consisted of three technical work-packages plus one management work-package. The three technical WPs tackle planning and realisation of possible design-changes, dynamic characterization and experimental tests (including post-processing). A crucial point for the quality of the results is the choice of the wind-tunnel. Possible wind-tunnels in Europe have been reviewed by the consortium and the two possible solutions for this model (DNW and RUAG) have been asked for quotes. Although the previous model was built for an aerodynamical measurement campaign in one of these tunnels, in general a test in either of them is feasible. There are pros and cons for each solution, finalising the choice of the wind-tunnel is therefore the first point to tackle in the project.


Parent Programmes
Institution Type
Public institution
Institution Name
European Commission
Type of funding
Public (EU)
Specific funding programme
JTI-CS - Joint Technology Initiatives - Clean Sky
Other Programme
JTI-CS-2013-2-GRA-02-025 Highly-accurate/reliable WT tests community noise assessment of an Advanced TP Regional A/C integrating HLD innovative low-noise design


Executive Summary:

In WITTINESS, noise-characterisation of low-noise technologies developed within the frame of the GRA-ITD in Cleansky 1 was performed. In order to do this a Wind-Tunnel model, which was developed in the frame of the Cleansky-project LOSITA, was used. Within WITTINESS the partners University of Rome 3, REVOIND Industriale and IBK were implemented. REVOIND Industriale was later replaced by EUROTECH.

In order to perform the test-activities, specific requirements for the tests and the WT-model needed to be defined. Due to the fact that the model is large (span of 4.9m) all activities needed to be planned with care including logistics onsite in the WT. The WT was chosen to be the RUAG Large-Wind Tunnel in Emmen.

In order to optimise and de-risk activities the design and manufacturing of the LOSITA was done on strong cooperation with the EASIER project thus taking into account acoustic requirements, like:

- Different configuration in the WT (dorsal vs. ventral), model needs to be rotated

- Landing-gear bay to be realized in a way that is representative of real acoustics

were taken into account upfront and did not lead to a design solution that would impact either test.

Within LOSITA the test-setup was defined and tested in the WT in an isolated environment. A setup including sideline microphones, a beamforming array and specific locations to position the array was defined and validated during the pre-tests. A microphone was used as a model during the pre-test, thus allowing generating a defined noise and making sure that the post-procession actually works. The pre-test was successfully performed, important lessons learned for the main test were obtained.

After model availability the tests were performed in the RUAG-Wind-Tunnel using a test-matrix defined together with the Topic Manager. The Wind-Tunnel tests were performed as planned, allowing a characterisation of the noise acting on the wing and analysing the effect of low-noise technologies developed.

Project Context and Objectives:

Throughout the late 1970s and early 1980s, NASA engineers worked on an effort dubbed "the Advanced Turboprop Project"- a US government-funded study to examine the feasibility of developing the turboprop engine as a viable competitor to the larger, less efficient turbojet and turbofan designs found on airliners of the day. The studies showed that the turboprop configurations were very efficient at cruise speeds up to about Mach 0.65 providing a fuel savings between 10 to 20 percent with respect to equivalent technology turbofan aircraft. On the other hand, above this speed, the increased drag due to compressibility losses on the propeller blades causes efficiency to fall rapidly. One way to lower compressibility losses is to increase the Mach number at which drag rise occurs by using thinner airfoil sections. In the past, when the fabrication was limited to metal blades, the construction of very thin blades was not possible and the development of high speed turboprop aircrafts stopped leaving space to turbofan configuration. Now, with the use of composite materials and advanced construction techniques, it is possible to construct blades with thinner airfoil sections and more optimum shapes (sweeping the blade leading edge, scimitar geometry, etc) that can operate in high subsonic conditions (up to M=0.8). Therefore, taking into account the fuel saving and the lower operating costs, the optimization of the turboprop configuration is going to become again one of the most important matter of research studies. This is widely demonstrated by the strong interest that the main international agencies are dedicating to the design of advanced Turbo-prop aircrafts. The main research branches are focused on the design of high efficiency and low noise configuration, on the fuselage noise attenuations for passenger comfort, on the design of innovative and high efficient propellers, and on the optimization of the engine-airframe integration.

Within this context, special care is dedicated to both the improvement of aerodynamic performances and the reduction of the environmental noise impact of turbo prop regional aircraft mainly in take-off and landing condition.

Aircraft noise is getting major interest by the scientific community due to the effort in reducing sky-traffic acoustic pollution in the airport area. Aircraft landing gear, propeller and high lift devices (HLD) have been recognized in recent years as responsible of the major contributors to the total aircraft noise, especially at landing and take-off conditions. After a period of improvements on low noise engines, the attention has been, nowadays, shifted on the study of the airframe aerodynamics. This is particularly challenging for turboprop A/C configuration because of the large interaction between the slipstream generated by the blades and wings/airframe and between the landing gears and fuselage. Modern computation methods are mainly based on ideal fluid theory, and are not able to fully reveal and take into account the above-mentioned effects. Therefore, the numerical prediction of these sources of noise remains one of the most difficult challenges in aero-acoustics, because of the complexity of the gear and propeller geometries and the surrounding flow field. Experimental activities are, therefore, the main way to study the acoustic performances of propellers and airframe/landing gears interaction, to assess the magnitude of the noise sources and to develop an analytical and experimental data base for numerical comparisons.

Wind tunnel tests on turboprop configurations often use unpowered models which are only able to provide partial information of the acoustic performance of the aircraft without considering the interactions between the propulsion system and both the airframe and aerodynamic surfaces (wings, HLD, fuselage and empennage). Propeller noise is, thus, measured in separate tests. To provide more accurate experimental estimates of the overall acoustic performances, challenging experimental tests using active propellers are necessary. The main innovative aspect of the present project is, in fact, the noise assessment of an Advanced Turbo Prop Regional Aircraft by means of wind tunnel tests on a complete and powered aircraft model. A further innovative aspect is the assessment of the novel “lined flap” architecture in airframe noise reduction Tests are planned on the model equipped with both the standard flap architecture and the “lined flap”.

The following Wind tunnel tests were performed with the objective:

• to evaluate at take-off and landing conditions the whole A/C noise emission in far-field measured by a moveable microphone array;

• to identify in the same conditions the noise sources by means of a beamforming technique and their contribution to the emitted noise.

• to verify the effect of a lined flap on the overall noise reduction;

In order to fulfill these goals, the WITTINESS project was split in the following technical activities:

I. Model modifications to fulfill WT requirements for acoustic tests.

II. FEM model creation and validation

III. WT instrumentation definition

IV. WT test campaign.

V. Data processing and analysis

Acoustic tests were performed on a WT model designed and manufactured within a previous project LOSITA. The main outcome of the LOSITA project (managed by IBK) is the aerodynamic assessment of the overall turbo prop regional A/C configuration in take-off and landing conditions. Tests will be performed on a complete A/C model powered by two wing-mounted engine simulators. To satisfy thrust requirements and to overcome life duration and heat problems, the selected scheme will use engine simulators powered by a hydraulic system able to set and keep thrust within 5% of the target value. Within the LOSITA proposal, aerodynamic tests are planned in the Large Wind Tunnel Emmen (LWTE) of RUAG (partner of the LOSITA consortium) where a suitable hydraulic infrastructure (4 pumps of 1000kW total power is available. The same WT will be used in this project. The aerodynamic test campaign will focus on the optimization/estimation of the aircraft configuration (in terms of nacelle shape, trailing edge devices, movable surfaces, etc.) and on the validation of the resulting overall optimized aircraft architecture from an aerodynamic point of view.

Aero-acoustic tests foreseen within the present project will therefore complete the assessment of the GRA turboprop A/C configuration also for what concerns the noise emission.

Often, open jet wind tunnels are used to perform experimental aero-acoustic investigations. These facilities allow out-of-flow far-field acoustic measurements, significantly improving individual microphone signal-to-noise ratio. Additionally, these facilities can be realized in anechoic chambers, thereby permitting acoustic level analysis without contamination from acoustic reflections. However, the open-jet configuration comes at the cost of additional flow-induced disturbances. Such disturbances include (non-comprehensive list):

▪ Edge noise from the open test section entrance/contraction exit.

▪ Free shear-layer noise.

▪ Shear layer/collector interaction noise.

▪ Model-facility interactions, such as core flow deflection in high-lift configuration.

▪ Shear layer effect on sound propagation path

These effects can manifest themselves as real acoustic fluctuations at a single microphone and they can be mitigated by using a multiple-microphone processing technique. Phased microphone arrays have become an important tool in aeroacoustic testing for their ability to localize and quantify different noise sources. The identification of noise sources is based on the principle of the differences in path lengths between a particular source position and the individual array microphones. As result of the difference in propagation time, each microphone receives a signal with different phase. In principle, the microphone signals are individually delayed by these pre-calculated "phase differences" and summed up to provide the noise level at the considered location in space (for each frequency band of interest). This calculation is performed repeatedly for every location of interest in space and thus results in a complete source map. The array must be optimized in size and microphone distribution to provide a satisfactory signal-to-noise ratio, frequency range and geometric resolution for the given geometry of the setup in the wind tunnel.

Microphones arrays are used in wind tunnels and in the field, and can be applied to stationary and moving objects. However, while the source location using phased microphone array has become a standard technique in aero-acoustics, the quantification of array results is still far from straightforward. First, aero-acoustic noise sources are often not point-sources but spread over a certain area (e.g. slat noise, trailing edge noise). As a consequence, the peak levels in the source map depend on the extent and coherence of the source region and on the (frequency-dependent) resolution of the array. Second, the levels may be influenced by coherence loss between the microphones. Coherence loss can occur when sound is scattered by turbulence (e.g. in the shear layer of an open jet wind tunnel), and typically results in broader lobes with a reduced level on the source map compared to the correct value.

Some of the above reported problems can be overcome by using closed test section wind tunnels. Today, these wind tunnels are regularly used for acoustic array measurements since recent research activities evidenced that phased array technique for quantifying airframe noise can be performed in both closed and open jet wind tunnel, providing similar source characteristics. Results showed that in the closed test section coherence loss effects seemed to be small, but measurements are affected by flow noise on the wall-mounted array microphones and by the turbulent boundary layer from test section sidewalls. This doesn’t represent a problem since this is well understood and correction methods have been developed which are applied to remove these uncorrelated noise components. In general, lower integrated noise levels are measured in open jet wind tunnels with microphone arrays than in closed test sections (probably due to coherence loss effects); the relative levels - compared to a measurement within a reference model configuration - are very similar for both test section types.

Another point to be addressed is the approach of using hydraulic engines in an acoustic test. They are often referred to as “noisy”, however, different tests in the past were able to show that these engines are a perfect solution for acoustic tests. The main argument for this is to be found in the characteristics of the acoustic test. Generally, due to the characteristics of the human ear and the atmospheric propagation/damping, noise assessments are made in the frequency range of 150Hz to 3 kHz. Transferred to a model scale of 1:7 this results in a working range for acoustics of 1050Hz to 21kHz. Independently of the wind tunnel, the geometric resolution of array measurements falls off quickly to unacceptable levels (1m and more) below 1kHz (integrated noise levels are still possible but the noise source location cannot be resolved). Thus a model scale of 1:7 is acoustically ideal. The hydraulic engines that are used are running at a maximum speed of 9000 RPM, corresponding to 150 Hz. These engines therefore work in a totally different frequency range and are very nicely separated from the frequency region of interest. Since hydraulic engines normally run at lower speeds than (for example) pneumatic turbines (current turbines run at 15'000rpm and well above) the use of hydraulic engines actually increases the frequency distance between the engine disturbance and the measurement range. Another practical advantage of hydraulic engines compared to air turbines is that the temperatures can be kept at a "normal" and constant level, intrinsically preventing the icing risk of air turbines (also with benefit to balance measurements).

Project Results:

Main S&T results/ foreground

The following scientific and technical results have been identified:


- University of Rome 3 has developed a method that allows calculating correct EPNL from test-results obtained by closed-wall wind tunnels. This is a very innovative solution for the problem of noise characterisation and allows using closed-wall WT in the future. The advantage of this approach is that these WT are less costly as dedicated WTs and have a higher availability.


- Within WITTINESS, technologies have been developed on how to perform noise-characterisations on powered WT-models. Although during the WT-tests the engine in WITTINESS was not running (due to requirements from TM) it is possible and allows an improved acoustic result.

- In WITTINESS there was a need to quickly rotate the model after the aerodynamic test campaign to implement it into the acoustic configuration. This was realised after strong discussions with RUAG in a very efficient way, reducing the WT-blocking time and improving in total the output.

- WITTINESS performed the noise-assessment for the lined flap technology developed in the CS-GRA ITD. It can be seen that the application of the flap-fence is able to reduce the noise emitted during the landing/ takeoff phase.

- In WITTINESS acoustic characterisation of a model involving running engines was performed for the first time in the RUAG-WT. This enhances capabilities of RUAG (not partner in WITTINESS, but in LOSITA).

Potential Impact:

Bringing together complementary, in terms of competencies, SMEs and one university, allowed for commonalities to be identified and opened the possibility for cross-domain sharing of concepts, methods and tools in order to enable reusable embedded technology development. In addition, WITTINESS consortium cooperated with one of the largest European Wind Tunnel with extensive experience in acoustic aircraft models testing. These transversal competences, added to the specific competences of the involved SMEs, enabled the consortium to be extremely confident about solving any critical problem that requires interdisciplinary expertise, thus allowing WITTINESS to address any technological innovation and/or any model modification. This cooperation between partners enriched their knowledge and their capability in design, manufacturing and testing. This allowed increasing the competitiveness of the European aeronautical industries in the world.

The impact of this project will work on several different levels:

• Regarding JTI-Cleansky, this project helped in solving important questions concerning the noise emission in landing and take-off and off-flight conditions. In fact, the project aim to investigate the acoustic performance in high lift condition of the new green turbo prop aircraft model equipped with devices, such as the liner flap, able to reduce noise and their application on future Green Regional Aircraft. On an international level, this increases Europe’s competitiveness in the development of the future Green Turbo prop regional aircraft, since the landing and take-off flight conditions are the noisiest conditions. Suitable high lift system, able to guarantee aerodynamic performance and to reduce noise emission (such as Liner technology) and optimized winglets will contribute to further improve the performance of this new Green Regional Aircraft allowing to match the future ACARE 2020 goals.

• Apart from at national level, each partner that contributes to the project has several advantages:

o Insight into high fidelity test results for an advanced technology aircraft wing

o A reference project that shows competence on an international level as well as successfully working together as a multi-disciplinary team

o All partners in the consortium have the opportunity to further increase their know-how by working in synergy and in an international context. In case of the SMEs this can be further exploited by transferring IP generated in this project into industrial applications.

o The SMEs will strongly interacted with one of the largest European Wind Tunnel's and this provided a formidable chance to enrich their expertise

o WITTINESS consortium members such as IBK are giving lectures at universities. This allows transferring knowledge achieved in this project to future engineering generations.

This will contribute to increase the competitiveness of the European aeronautical industries because they will have a facility that can also simulate landing and take-off conditions by using engine simulators for turbo prop aircraft configurations.

Socio-Economic Impact/Wider societal impact:

Due to the strong technical focus of this project the direct socio-economic impact of this project is limited.

Indirectly IBK as well as EUROTECH as SME´s are seeing gender equality as one of the relevant topics for their human-resource strategy. Within IBK ~30% of the employees are female (seen over all technical units). IBK is very supportive in enabling work-life balance, especially supporting young families with part-time jobs. This helps to keep young and very skilled professionals in the company, provides a good internal climate and a forward oriented mind-set.

Being able to positively support these projects as SME is therefore supporting IBK´s and EUROTECH´s strategies.


All work packages will after finishing the technical work in the project undergo an internal checks from each partner for exploitation. The management of knowledge and intellectual property, as well as the establishment of exploitation and dissemination strategies will be dedicated

− To manage the generated knowledge and confidentially-related issues.

− To identify the results that can be disseminated (through publications, conferences, workshops, technology transfers)

− To identify results that should be protected (through patents, copyrights or secret) and - if necessary - to achieve an agreement in case of joint ownership.

− To analyse end-user requirements and a potential market as an exploitation strategy.

− Intellectual Property Rights and dissemination of knowledge are not incompatible, provided that they are based on clear principles and rules.

Ownership of results, mutual granting of access rights, IP protection (including patenting) and licensing policy has been defined in a Consortium Agreement between the three participants.

Currently the following items have been identified for further exploitation:

- University of Rome has developed a method that allows calculating correct EPNL from test-results obtained by closed-wall wind tunnels. This is a very innovative solution for the problem of noise characterisation and allows using closed-wall WT in the future. The advantage of this approach is that these WT are less costly as dedicated WTs and have a higher availability.

- Within WITTINESS, technologies have been developed on how to perform noise-characterisations on powered WT-models.

- In WITTINESS there was a need to quickly rotate the model after the aerodynamic test campaign to implement it into the acoustic configuration. This was realised after strong discussions with RUAG in a very efficient way, reducing the WT-blocking time and improving in total the output.

- In WITTINESS the acoustic tests were performed with running engines. This was the first application within the RUAG-WT.

Contach Details:

Dr.-Ing Stephan Adden

IBK-Innovation GmbH & Co. KG

Butendeichsweg 2

21129 Hamburg


Lead Organisation
Ibk-Innovation Gmbh & Co. Kg
Organisation website
EU Contribution
€411 804
Partner Organisations
Revoind Industriale
Organisation website
EU Contribution
€189 128
Eurotech Di Mario Amoroso Sas
Via Luigi Mercantini 23 IS 8, 80125 NAPOLI, Italy
Organisation website
EU Contribution
€30 150
Universita Degli Studi Roma Tre
Via Ostiense 159, 154 Roma, Italy
EU Contribution
€116 670


Technology Theme
Noise testing, modelling and reduction
Engine core noise measurements
Development phase
Demonstration/prototyping/Pilot Production

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