Final Report Summary - TEENI (Turboshaft engine exhaust noise identification)
Executive Summary:
The 'Turboshaft engine exhaust noise identification' (TEENI) was a level one Seventh Framework Programme (FP7), first call project, with 11 partners (Turbomeca - Coordinator, ANOTEC, AVIO, Brüel and Kjaër, Comoti, DLR, EPFL, INASCO, Microflown, ONERA, TCD), for an overall European Community (EC) funding of EUR 3.3 million. It has been launched on 1 April 2008, for initial three years duration, finally extended to five years.
TEENI was dealing with experimental identification of engine modules' responsibilities on exhaust Broadband Noise emission. This noise component is the second dominant noise source of a turboshaft engine and installing acoustic liners on the exhaust can lead to significant noise benefit on the whole helicopter levels.
Turboshaft exhaust noise is assumed to be a mix between combustion and turbine noise, with very little jet noise. It is representative of what is generally called core noise on aircraft engines. TEENI should help to understand this difficult subject as well, thanks to its simpler geometry and absence of strong parasitic noise sources (such as jet and fan noises).
TEENI work programme was divided in three inter-dependent work packages (WP):
1. WP1: Innovative sensors development, to provide reference measurements of fluctuating quantities within the engine, under its harsh conditions
2. WP2: Noise sources breakdown techniques (NSBT) development, to determine the dominant emission location from external measurements. Several techniques were evaluated, considering internal and external measurement, as well as various formalisms and approaches. Propagation through turbine(s) has been studied and tools to help taking into account individual engine noise sources have been also developed.
3. WP3: An Ardiden-1H1 turboshaft engine full-scale test, which included the developed sensors, was used to verify (through correlation with internal sensors) and assess the various NSBT pertinence and provide a first example of noise decomposition per module.
In order to reduce development risks, both sensors and methods were tested within their relative WP before the engine test.
The TEENI project suffered from a poor estimation of engine new instrumentation implementation difficulty: task was so complex that most of the rear (from combustion chamber to power turbine) casings needed to be completely re-designed and manufactured from scratch. This required the project to be extended to overall five years duration.
Testing was finally successful, with a very good behaviour of the new engine parts and the new installed instrumentation and measured data was analysed.
The major deliverables of TEENI are:
1. pressure and temperature probes for measuring unsteady quantities, adequate for full-scale engine testing (650°
3. a noise breakdown realised out of a panel of original signal processing methods which have been developed during the project, using internal measurements to understand the origin of noise measured in the farfield
4. elements of understanding of noise generation, propagation and radiation through the exhaust, from experimental and theoretical point of view.
Combustion noise was identified at low frequencies and its relative importance is shown to be increased after the HP Turbine. The influence of power turbine, very important at high frequencies, was more difficult to stress in the TEENI frequency band of interest (0 to 4kHz). However, broadband noise origin for frequencies above 2kHz was not fully explained.
Project Context and Objectives:
TEENI deals with understanding aeronautical noise, in particular helicopters noise, with the goal of an increased noise reduction in mind.
As engine noise is a main contributor to the whole helicopter exterior noise and as exhaust noise still needs an increased attenuation, this project focuses on understanding exhaust noise sources.
TEENI's four objectives are intimately linked towards the final goal of this project: to determine on which noise source a turboshaft exhaust liner should be optimised. Each objective is further discussed in the following paragraphs.
First objective: To discriminate the helicopter engine noise sources
Today's helicopters need to be improved further with respect to environmental and public acceptance. Helicopters can generate a large amount of external noise, which can be aggressively perceived, as helicopter's traditional missions -rescue, medical, law enforcement- are by essence very close to populated areas. As emphasised in ACARE SRA2, the existing tendency to increase rotorcraft missions in the public vicinity should not lead to an increase of public disturbance.
Main exterior noise sources on helicopters include main rotor, tail rotor and engine. The relative weight of these noise sources varies with a large number of parameters, among which engine integration to the helicopter and flight profile are key players.
The turboshaft engine is generally known as a main contributor to exterior noise for take-off certification conditions. As helicopter manufacturers are nowadays seeking at least two engine providers per helicopter series, diminishing engine noise levels also increases its competitiveness.
Noise can be significantly reduced thanks to adding acoustic liners on the engine intake or exhaust or by careful 'silent' design of the engine modules. Both solutions may prove to be interesting and they both need a precise diagnostic concerning the origin of the noise. Choosing between these two very different approaches implies a careful examination of noise/performance/weight/cost trade-off, which is not the subject of this study.
Up to now, main research efforts have been carried out towards understanding and cancelling centrifugal compressor noise. Good results have been obtained so far in previous national and EC funded projects (Friendcopter) combining both installation effects and inlet liners.
Former EC research projects (Hortia, Silence(R)) have managed to reduce also significantly the noise coming out of the exhaust of the engine and to demonstrate the industrial evidence that a liner can be installed on the exhaust. An in-flight evaluation has even been realised in Friendcopter.
But, to comply with ACARE SRA2 objectives, this noise reduction has to be further maximised.
Even more crucial in the exhaust case, it becomes a requirement to understand the noise sound sources origin and development. The interest mainly lies in exhaust broadband noise identification, as turbine tones can be easily identified, their frequencies being a multiple of the number of rotor blades. Moreover, these tones are generally beyond frequencies of interest, due to the high rotation speed and high blade number.
Tackling broadband noise identification subject is an ambitious goal, due to the complexity of the physics involved, the severe environmental conditions in the engine hot parts and exhaust which prevent from using standard instrumentation and the (small) available space on this kind of engines. It is critical to be able to assess which of the engine noise contributions is the most important in flight.
All the techniques developed within this project are needed to accomplish this first objective.
Second objective: To provide an instrumentation breakthrough
Existing sensors for fluctuating (unstationnary) quantities such as pressure, acoustic velocity and temperature are not fully reliable within the temperature range of interest (>650°C) when mounted on engine casings, as shown during the Silence(R) project. Such sensors are true enablers for the investigation of generation and propagation of sound in the exhaust hot duct.
Recent sensor developments have shown new generation products, using innovative materials that may prove to be useful towards the targeted temperature range. This provides the confidence for proposing now to develop such hi-tech sensors.
The consortium of TEENI relies extensively on instrumentation, internal and external, to diagnose noise origin through correlation -and more advanced- techniques.
For the case of instrumentation development, this project is somewhere in the middle between a research project and a demonstration project, as technologies have to be developed, tested in laboratory under 'realistic conditions', before they can be used on an engine test to provide the needed data of interest.
Third objective: To understand the noise propagation through blade rows
However, measurements alone will not be sufficient. There is also a need for the physical understanding of the complex mechanisms linked to:
1. noise generation within the combustion chamber
2. noise generation within the turbine stages
3. noise propagation through the turbine blade rows.
A dedicated experiment will focus on these aspects. Its output will help to analyse the results of the full-scale engine test and will bring assurance that TEENI's findings can be generalised further.
Fourth objective: To provide innovative exhaust noise sources breakdown techniques
Whereas most of noise sources breakdown techniques focus on 'visible' noise sources, our purpose is to be able to attribute to each engine module (combustor, high pressure turbine, power turbine) its responsibility in terms of radiated noise. All these contributors are 'hidden' within the engine casings, hence the need to push existing techniques much further, using the newest methods in signal processing.
TEENI's objectives can be summarised as follows:
1. to discriminate the origin of the sound field radiated from a turboshaft engine's exhaust and highlight the priorities for exhaust liners optimisation on the most prominent engine noise source in flight.
In order to achieve this ambitious goal, it is necessary:
1. to develop and test sensors, adapted to fluctuating quantities (such as acoustic pressure, acoustic velocity, temperature fluctuations etc.) and resistant to the engine environment (temperature, grasing flow)
2. to understand how does the broadband noise propagates through turbine blade rows
3. to develop and apply noise sources breakdown techniques able to locate the noise origin from inside the engine casings.
Project Results:
Turbomeca
Tones cut-off method
This method has been developed within the Turbomeca tool for analysing test data, called LEDA. It will enable a thorough treatment of the whole database, enabling a more precise update of semi-empirical methods for noise prediction.
Broadband noise decomposition tool
This method, developed by Anotec is also included in Turbomeca LEDA software. The purpose is the same as the one above, but applied to broadband noise.
Ardiden 1H1 TEENI database
Tests realised in WP3 represent a very important database, with synchronised internal and external measurements, on the basis of which our knowledge of noise sources has been and will be challenged.
Already analysed in this project, data will be used again in the Record project to compare with calculations realised under the same conditions.
Decomposition methods applied by partners
Methods developed within WP2 and applied to full-scale engine test data enabled to build a first noise decomposition. This decomposition will act as a basis for analysing the whole Turbomeca database.
Anotec
Broadband noise decomposition tool
This method has been developed by Anotec within the above-mentioned LEDA tool developed by Turbomeca for analysing test data. Based on the broadband noise predictions from other TEENI tools it will enable a thorough treatment of the whole database, enabling a more precise update of semi-empirical methods for noise prediction.
Interface with Helena helicopter noise prediction platform
An interface was developed that makes it possible to use the results from the noise source decomposition, performed by LEDA, directly as input to the Helena helicopter noise prediction platform. This allows for a better assessment of the contribution of each engine noise source to the total helicopter noise and as such will assist in focussing efforts on reduction of the most relevant noise sources.
Avio
Method for broadband noise propagation through turbine rows
Within TEENI Avio has extended the existing tone noise analysis method to broadband noise propagation studies. This method is based on a time-linearised approach and assumes that the sound field generated by the interaction of a blade row with vortical and pressure disturbances coming from adjacent rows is a small perturbation of the background flow field. The extension proposed for the present investigation is based on the assumption that a broadband noise field can be seen as a superposition of an infinite number of uncorrelated modes, differing one another for the frequency value and /or the azimuthal and radial shape. These perturbations can be thus independently solved and finally summed together within the small perturbation hypothesis.
Systematic calculation of transmission /reflection coefficients
A significant amount of Civil Aviation Authority (CAA) simulations has been performed taking into account different turbine rows in order to calculate the acoustic response to selected incoming cut-on acoustic mode (circumferential as well as radial mode orders). Final result of this activity has been the calculation of transmission curves as a function of acoustic frequency and modal order. These curves work as transfer function and describe the acoustic interaction between the incoming wave and the row enabling the identification of correlation between the acoustic properties of the stator /rotor rows and the main geometric, aerodynamic and acoustic parameters (precious information in the early design phase).
Investigation on the applicability of quasi three-dimensional (Q3D) approximation
The introduction of the Q3D approximation (infinitesimal thickness duct) has been investigated as a way to reduce the computational time of the Bayesian belief network (BBN) propagation simulation. It turned out that this approximation gives sufficiently accurate results depending on the analysed frequency.
Bruël and Kjaër
Harmonic removal tools developed
A set of methods were developed to be able to solve the task of removing harmonic components from the time data recorded at the sensor positions. The output from the harmonic removal process constitutes broadband data to be further studied by noise source breakdown methods.
Blind source separation research
Research into blind source separation methodologies was conducted with the aim to pinpoint methods capable of solving the needs within the project. Several methods have been implemented based on already available code. The idea with the blind separation is to make the separation process simpler from a practical point of view.
Comoti
Sensor testing
Comoti carried out the experimental rig sensor testing for the microphone probes developed by DLR and the dielectric sensors developed by Inasco. The experimental program was aimed both at demonstrating that the new sensors can maintain structural integrity in the harsh environmental conditions (high temperature and pressure) to be expected in the hot region of a gas turbine engine and at providing reliable and accurate experimental data from independent measurement equipment, for the calibration of the new sensors.
The parallel measurements were carried out by means of temperature and pressure probes and particle image velocimetry and the database resulting from these experimental measurements forms a highly valuable foreground generated from the TEENI project. This database has already been used by two of Comoti's doctoral students for validation of their numerical works, in their respective theses and is expected to be further used for computational fluid dynamics (CFD) subroutines to be developed at Comoti, also as validation data. Two national research grant proposals on this subject are currently under evaluation.
Engine parts manufacturing
A second task Comoti was involved in was the manufacturing and design of new engine parts required for the adaptation of the helicopter engine used for final testing to the instrumentation required by the experimental program. The foreground generated by Comoti in this process was the optimisation of its manufacturing technologies, taking into account the high complexity of the parts that, due to the fact they were unique items, had to be manufactured from blocks, as no forged semi-finished parts existed, the budget and time constraints and the high strength, low manufacturability of the special materials required for the parts. The knowledge gained by Comoti in this activity will be further used for attracting and carrying out new design and manufacturing contracts, either economic, or in research grants.
DLR
High-pressure microphone probe
The newly developed microphone probe enables the assessment of acoustic pressure fluctuations up to an amplitude of 105 Pa even in harsh environment, i.e. at elevated pressure (up to 20bar above atmospheric pressure) and high temperature (e.g. in combustors with 1 200°C mean gas temperature). The probe can and will be used by the foreground owner (DLR) for acoustic investigations in model and full-scale aero engines where conventional instrumentation cannot be used. It will be also used in a dedicated hot-acoustic testrig of DLR for accurate assessment of acoustic dampers (so called liners) tested at elevated pressure and temperature. This testrig - together with the new probes - bridges the gap between commonly used cold-and-atmospheric investigations and the actual aero-engine application of these dampers, thereby adding valuable knowledge for the research community as well as validation data for the design tools of aero engine manufacturers.
Future investigations and development regarding this probe type will aim at better understanding of high pressure behaviour and also at reduced size and weight for even more simple installation in complex test setups.
New method for noise source discrimination
The new method for noise source discrimination will be used by the owner (DLR) for future research projects dealing with internal noise propagation in complex systems such as compressor and turbine stages. It is of great importance for better understanding the noise generation, propagation and specific effects such as frequency scattering or indirect combustion noise when the sound field is not easily accessible due to space and other constraints. With the findings of this analysis method it is possible to better distinguish between different noise sources present, weight their respective importance and adapt counter-measures (such as acoustic dampers) to the most relevant sources. Results of these research projects are frequently published at international conferences and journals, thereby adding to the knowledge of the scientific community.
EPFL
External sound source separation techniques
The enhanced acoustic goniometer is a specifically designed device, composed of geometrically arranged microphones ('array') to observe sound fields from a defined spatial solid angle. Here the design has been oriented towards focusing on the direct sound radiated by the turbine, excluding external noise contributions uncorrelated with the turbine. In addition to this array, it has been decided to use in parallel an octahedral array of six microphones.
The technique is based on the estimation of different time delay of arrival (TDOA) on several couples of microphones within the array, extrapolated to derive directions of arrival (DOA). The TDOA are estimated through inter-sensor cross-correlation estimation, using different weighting functions on the cross-correlation to enhance the accuracy.
Preliminary testing in anechoic conditions and for multiple sources have proven the capability of the array to simultaneously detect and localise multiple sound sources. The different post-processing techniques have been compared, leading to specification of the array (and processing) design with respect to the nature and number of the sound sources.
Microphone and sensor testing
In the frame of TEENI project, a novel test-rig has been specifically developed for the assessment of the performances of fluctuating temperature sensors (DLR). It is composed of a spinning perforated disc and of an acetylene flame welder combined to obtain 18 fluctuations of temperature per rotation. Finally the rotation per minute (RPM) control permits to modulate the frequency of temperature fluctuations. The number of RPM is manually regulated via an amplifier; the real RPM is measured using one external laser tachometer giving a pulse per rotation. The final frequency bandwidth obtained is 36 Hz to 900 Hz. At low frequency the disc is not cooled enough due to the high temperature flame (T>3 000°C), at high frequency some damage could appear on the whole mechanism due to induced vibrations.
Following recommendation of Microflown partner, one short wave tube (SWT) has been designed to make some qualification of the Microflown sensor. The SWT is composed of one acoustic driver connected to one rectangular steel tube with one access for the MF sensor and one for the reference microphone. Using this acoustic set-up, the calculation of the sensitivity of the sensor is done in the 100 Hz to 4 000 Hz bandwidth for sound pressure level up to 130 dB.
Inasco
Design of high temperature velocity fluctuation sensor
In the TEENI project a high temperature sensing element (based on dielectric measurement) for flow velocity fluctuations is developed. The sensor will be used in a gas turbine engine, at temperatures of around 650 °C and wind speeds of in excess of 200 m/s.
The sensor element consists of a durable substrate as insulator and metal/alloy as signal conductor. The substrate is used to support the positioning of two plates over its surface. The metal plates create the area of a capacitor and the engine gas is expected to flow within the plates. The metal plates are also used for the transportation of the signal away of the sensor surface.
In the particular sensor configuration, the metal plates are partly inserted in the ceramic substrate and they have an aerodynamic shape with flat active face. The sensor dimensions can be easily adapted according to project needs and dielectric measurement requirements.
The sensor operation consists in the creation of a homogeneous electric field (of constant intensity) between the metal plates. The gas flows in a direction perpendicular to the electric field lines in parallel to the sensor substrate surface.
The developed sensor has been tested at extreme conditions at the exhaust of a small turbojet engine where temperatures are above 800 °C without any problem. Sensor safety and performance testing took place in Comoti, where the feasibility was proven without any problem. The test plan for the dielectric sensors involved the progressive rise of the temperature in the sensor vicinity to the highest possible limit in order to test the survivability of the sensor in extreme environment. The maximum obtainable temperature for this engine was T=900 °C. The sensors appeared to perform equally well at this temperature level as well as afterwards. The velocity reached 130 m/sec. Visual inspection and examination of the sensors confirmed their excellent condition.
Microflown Technologies
Improved design of Microflown acoustic particle velocity sensor
A novel cleanroom design of the Microflown acoustic particle velocity sensor was developed that can operate at elevated temperatures up to 600 degrees Celsius, the wires themselves reaching around 750 °C. The work was subcontracted to the University of Twente.
A novel acoustic far field sound source localisation technique
A novel acoustic far field sound source localisation technique was developed capable of localising sound sources in a 3D space. Most of the work was done by an industry PhD, defending his thesis later in 2013 at the Institute of Sound and Vibration Research in Southampton.
Onera
Three sensors technique
This technique developed by Onera has been adapted in order to characterise the internal sources radiated during the full scale tests carried out with the Ardiden. It makes possible to extract the sound power levels of a source region measured locally by two sensors from the power spectral density measured by a microphone in far field. Moreover, the quality of the results can be assessed by comparing the deviation of the phase at the output of the method to the null phase.
TCD
Coherence-Based Noise-Source Identification Techniques
Both novel and existing methods of noise-source identification which apply the coherence function between pairs of in-engine microphones and far-field measurements have been tested for their suitability in full-scale engine tests using a small-scale experimental rig, before being applied using the data acquired for the full-scale Ardiden engine tests. Development of these techniques has allowed for better discrimination between the contributions of individual noise-sources within the engine (combustor, high-pressure turbine etc.) to the modal content of the noise radiated through the engine exhaust, as well as the noise radiated into the far-field. These techniques only require that a few reference sensors be located close to each noise-source of interest, which is beneficial for a real turboshaft engine where space is limited and the duct geometry is complex. More accurate identification of each noise-source's contribution to this measured noise has allowed for a better understanding to the generation and propagation of noise within the engine and therefore the possibility of enhanced mitigation through better informed acoustic liner design and location.
Scattering of Noise on Interaction with Rotating Turbomachinery
As noise propagates in turboshaft or similar aeroengines, this noise will interact with several rotor-stator stages. Both scattering on frequency (through a rotor) and mode order (through a rotor or stator) are possible under certain conditions linked to the characteristics of the incident noise and the rotor/stator geometries and rotational speeds. This frequency scattering phenomenon has not been the focus of an experimental study however. As part of the TEENI project, a small-scale test rig was designed to focus on this scattering of noise and found that both tonal and other noise can be scattered in this way, suggesting the possibility of frequency scattering and even spectral overlapping of broader-band scattered noise downstream of a compressor/turbine stage in a real engine.
Potential Impact:
Turbomeca
TEENI is part of the process of re-design of Turbomeca semi-empirical methods. These methods, designed from experimental results, are crucial for the engine manufacturer: they can estimate noise levels from the very beginning of a project, when very little information is available. TEENI has delivered elementary methods for engine noise test database treatment, on the basis of which the methods upgrade will be made possible. For the case where two different engines manufacturers are competing on a new product, confidence in forecasted acoustic levels is essential.
Through the identification of noise sources origin, we should be able to design better optimised liners for exhaust noise reduction and/or find ways to reduce noise at source.
Anotec
TEENI contributes to the continuous improvement of the Helena platform, managed by the Helena consortium, of which Turbomeca, Onera and Anotec are partners. This will finally contribute to an increased understanding of helicopter noise and thus enable further noise reduction.
TEENI results will be leveraged to the Soprano platform, Anotecs' fixed wing aircraft noise prediction platform, widely used in Europe. The noise source decomposition algorithm can be adapted so as to be used in the so-called static-to-inflight projection technique, often used as part of the noise certification process. This will allow Anotec to extend the range of certification services provided.
Avio
The control of the acoustic emissions is nowadays a critical aspect for the competitiveness of any aero-engine. Within TEENI Avio has developed a numerical method for broadband noise investigation and performed an extensive numerical work on aero-engine as well as turbo-shaft turbines, in order to investigate phenomena such as turbine shielding, modal and frequency scattering, while assessing the capability of the method to simulate broadband noise propagation in turbomachinery. This work results in a deeper comprehension of important acoustic aspects, revised design rules and, finally, a higher competitiveness for the Avio products.
Bruël and Kjaër
The blind source separation research conducted by Brüel and Kjaer during TEENI project is seen as platform towards more easy and practical methods for noise source investigations in the industry leading to pinpointing the cause of excessive noise levels. Based on this information noise level reduction improvements can be targeted.
Comoti
One of the strategic interests of Comoti is pursuing its increase in visibility and prestige at international level and the increase in scientific proficiency and technical expertise of its research staff. The project benefitted this strategic goal by allowing a significant contribution in a very complex and highly visible research field. Comoti's position in the European scientific community was consolidated by the dissemination of the results through scientific papers and participation in conferences, fairs and exhibitions, increasing its attractiveness for European and Romanian industrial or academic partners for future joint research projects. It also contributed to enhancing the proven expertise required for participating in European research projects, thus the potential of Romanian research to attract European funding. In support of this, Comoti's research team involved in TEENI had been awarded, as coordinator, two new FP7 research grants related to noise reduction and flame stability under supersonic conditions.
Furthermore, the experimental testing database resulting as foreground from this project is and will further be, used, in partnership with the "Politehnica" University of Bucharest and the Technical University of Iasi, as validation database for the numerical studies carried out by their students.
EPFL
The main research activity of EPFL in TEENI was devoted to the development/adaptation of the existing acoustic goniometer to the technical problem of turboshaft engine exhaust noise sources identification. The main scientific outcome was the achievement of an external compact microphone array to identify and separate multiple concurrent wideband sound sources in a confined configuration. Thus it can readily be considered as a significant contribution to noise source identification in several industrial fields where intrusive instrumentation is not possible or not accessible.
It is also worth mentioning that such techniques also apply to different other engineering fields and several have been already envisaged by EPFL that could have a significant societal impact. Among others:
1. road vehicle pass-by monitoring and tracking techniques, with capability of counting and estimating speed and size of vehicles along inter-city road (Marmaroli Patrick, 'Bimodal sound source tracking applied to road traffic monitoring', EPFL Thesis, n° 5618 (2013)). It could then serve as a deployable tool for monitoring noise pollution as well and collecting statistics on urban/inter-urban pollution.
2. microphone arrays for an unmanned aerial vehicle (UAV) to localise in real time concurrent UAVs for collision avoidance.
Inasco
With the successful implementation of the developed sensors Inasco will be able to expand its line of products to another market, this of the high temperature velocity and its fluctuation measurements. It is envisaged that within the next five years the high temperature sensors would be mature enough to be introduced to the market.
This is part of the company's long term strategy to introduce this technology to other fields of market, additional to the current one of composite manufacturing. Further to finished products like sensors and measurement systems, the knowledge and experience gained within TEENI will help in expanding company's service offerings, especially in the field of noise reduction technologies.
Microflown Technologies
The novel acoustic vector sensor based acoustic far field sound source localisation technique has been industrialised and is for instance used for the in flight monitoring of engines of larger (US) unmanned aerial platforms.
From 2012 till 2020, we expect to sell around 2 000 sensor nodes for EUR 20 000 each, so EUR 40 million turnover, gross margins 80 %.
There are clear ideas on how to bring the high temperature Microflown sensor element up to a technology readiness level of eight, but it will need quite some financial commitment.
Estimated research and development (R&D) is still 20 manyears, so around EUR 3 million.
Onera
The data based collected during TEENI project will allow new developments of data processing techniques, aiming at better understand the mechanisms at the origin of the noise generated inside an engine.
TCD
The analysis methods applied during the TEENI project (both existing techniques and novel methods) can be applied in a wide variety of duct acoustics scenarios where noise-source identification is being investigated, such as other types of aeroengine. The enhanced understanding of noise scattering developed as part of the project has resulted in the identification and prediction of a potential cause of tonal and broadband noise scattering in aeroengines, which may be erroneously attributed to other noise-sources when linear propagation path assumptions are made.
List of Websites:
http://www.xnoise.eu/about-x-noise/projects/generation-2-projects/teeni/summary/
The 'Turboshaft engine exhaust noise identification' (TEENI) was a level one Seventh Framework Programme (FP7), first call project, with 11 partners (Turbomeca - Coordinator, ANOTEC, AVIO, Brüel and Kjaër, Comoti, DLR, EPFL, INASCO, Microflown, ONERA, TCD), for an overall European Community (EC) funding of EUR 3.3 million. It has been launched on 1 April 2008, for initial three years duration, finally extended to five years.
TEENI was dealing with experimental identification of engine modules' responsibilities on exhaust Broadband Noise emission. This noise component is the second dominant noise source of a turboshaft engine and installing acoustic liners on the exhaust can lead to significant noise benefit on the whole helicopter levels.
Turboshaft exhaust noise is assumed to be a mix between combustion and turbine noise, with very little jet noise. It is representative of what is generally called core noise on aircraft engines. TEENI should help to understand this difficult subject as well, thanks to its simpler geometry and absence of strong parasitic noise sources (such as jet and fan noises).
TEENI work programme was divided in three inter-dependent work packages (WP):
1. WP1: Innovative sensors development, to provide reference measurements of fluctuating quantities within the engine, under its harsh conditions
2. WP2: Noise sources breakdown techniques (NSBT) development, to determine the dominant emission location from external measurements. Several techniques were evaluated, considering internal and external measurement, as well as various formalisms and approaches. Propagation through turbine(s) has been studied and tools to help taking into account individual engine noise sources have been also developed.
3. WP3: An Ardiden-1H1 turboshaft engine full-scale test, which included the developed sensors, was used to verify (through correlation with internal sensors) and assess the various NSBT pertinence and provide a first example of noise decomposition per module.
In order to reduce development risks, both sensors and methods were tested within their relative WP before the engine test.
The TEENI project suffered from a poor estimation of engine new instrumentation implementation difficulty: task was so complex that most of the rear (from combustion chamber to power turbine) casings needed to be completely re-designed and manufactured from scratch. This required the project to be extended to overall five years duration.
Testing was finally successful, with a very good behaviour of the new engine parts and the new installed instrumentation and measured data was analysed.
The major deliverables of TEENI are:
1. pressure and temperature probes for measuring unsteady quantities, adequate for full-scale engine testing (650°
3. a noise breakdown realised out of a panel of original signal processing methods which have been developed during the project, using internal measurements to understand the origin of noise measured in the farfield
4. elements of understanding of noise generation, propagation and radiation through the exhaust, from experimental and theoretical point of view.
Combustion noise was identified at low frequencies and its relative importance is shown to be increased after the HP Turbine. The influence of power turbine, very important at high frequencies, was more difficult to stress in the TEENI frequency band of interest (0 to 4kHz). However, broadband noise origin for frequencies above 2kHz was not fully explained.
Project Context and Objectives:
TEENI deals with understanding aeronautical noise, in particular helicopters noise, with the goal of an increased noise reduction in mind.
As engine noise is a main contributor to the whole helicopter exterior noise and as exhaust noise still needs an increased attenuation, this project focuses on understanding exhaust noise sources.
TEENI's four objectives are intimately linked towards the final goal of this project: to determine on which noise source a turboshaft exhaust liner should be optimised. Each objective is further discussed in the following paragraphs.
First objective: To discriminate the helicopter engine noise sources
Today's helicopters need to be improved further with respect to environmental and public acceptance. Helicopters can generate a large amount of external noise, which can be aggressively perceived, as helicopter's traditional missions -rescue, medical, law enforcement- are by essence very close to populated areas. As emphasised in ACARE SRA2, the existing tendency to increase rotorcraft missions in the public vicinity should not lead to an increase of public disturbance.
Main exterior noise sources on helicopters include main rotor, tail rotor and engine. The relative weight of these noise sources varies with a large number of parameters, among which engine integration to the helicopter and flight profile are key players.
The turboshaft engine is generally known as a main contributor to exterior noise for take-off certification conditions. As helicopter manufacturers are nowadays seeking at least two engine providers per helicopter series, diminishing engine noise levels also increases its competitiveness.
Noise can be significantly reduced thanks to adding acoustic liners on the engine intake or exhaust or by careful 'silent' design of the engine modules. Both solutions may prove to be interesting and they both need a precise diagnostic concerning the origin of the noise. Choosing between these two very different approaches implies a careful examination of noise/performance/weight/cost trade-off, which is not the subject of this study.
Up to now, main research efforts have been carried out towards understanding and cancelling centrifugal compressor noise. Good results have been obtained so far in previous national and EC funded projects (Friendcopter) combining both installation effects and inlet liners.
Former EC research projects (Hortia, Silence(R)) have managed to reduce also significantly the noise coming out of the exhaust of the engine and to demonstrate the industrial evidence that a liner can be installed on the exhaust. An in-flight evaluation has even been realised in Friendcopter.
But, to comply with ACARE SRA2 objectives, this noise reduction has to be further maximised.
Even more crucial in the exhaust case, it becomes a requirement to understand the noise sound sources origin and development. The interest mainly lies in exhaust broadband noise identification, as turbine tones can be easily identified, their frequencies being a multiple of the number of rotor blades. Moreover, these tones are generally beyond frequencies of interest, due to the high rotation speed and high blade number.
Tackling broadband noise identification subject is an ambitious goal, due to the complexity of the physics involved, the severe environmental conditions in the engine hot parts and exhaust which prevent from using standard instrumentation and the (small) available space on this kind of engines. It is critical to be able to assess which of the engine noise contributions is the most important in flight.
All the techniques developed within this project are needed to accomplish this first objective.
Second objective: To provide an instrumentation breakthrough
Existing sensors for fluctuating (unstationnary) quantities such as pressure, acoustic velocity and temperature are not fully reliable within the temperature range of interest (>650°C) when mounted on engine casings, as shown during the Silence(R) project. Such sensors are true enablers for the investigation of generation and propagation of sound in the exhaust hot duct.
Recent sensor developments have shown new generation products, using innovative materials that may prove to be useful towards the targeted temperature range. This provides the confidence for proposing now to develop such hi-tech sensors.
The consortium of TEENI relies extensively on instrumentation, internal and external, to diagnose noise origin through correlation -and more advanced- techniques.
For the case of instrumentation development, this project is somewhere in the middle between a research project and a demonstration project, as technologies have to be developed, tested in laboratory under 'realistic conditions', before they can be used on an engine test to provide the needed data of interest.
Third objective: To understand the noise propagation through blade rows
However, measurements alone will not be sufficient. There is also a need for the physical understanding of the complex mechanisms linked to:
1. noise generation within the combustion chamber
2. noise generation within the turbine stages
3. noise propagation through the turbine blade rows.
A dedicated experiment will focus on these aspects. Its output will help to analyse the results of the full-scale engine test and will bring assurance that TEENI's findings can be generalised further.
Fourth objective: To provide innovative exhaust noise sources breakdown techniques
Whereas most of noise sources breakdown techniques focus on 'visible' noise sources, our purpose is to be able to attribute to each engine module (combustor, high pressure turbine, power turbine) its responsibility in terms of radiated noise. All these contributors are 'hidden' within the engine casings, hence the need to push existing techniques much further, using the newest methods in signal processing.
TEENI's objectives can be summarised as follows:
1. to discriminate the origin of the sound field radiated from a turboshaft engine's exhaust and highlight the priorities for exhaust liners optimisation on the most prominent engine noise source in flight.
In order to achieve this ambitious goal, it is necessary:
1. to develop and test sensors, adapted to fluctuating quantities (such as acoustic pressure, acoustic velocity, temperature fluctuations etc.) and resistant to the engine environment (temperature, grasing flow)
2. to understand how does the broadband noise propagates through turbine blade rows
3. to develop and apply noise sources breakdown techniques able to locate the noise origin from inside the engine casings.
Project Results:
Turbomeca
Tones cut-off method
This method has been developed within the Turbomeca tool for analysing test data, called LEDA. It will enable a thorough treatment of the whole database, enabling a more precise update of semi-empirical methods for noise prediction.
Broadband noise decomposition tool
This method, developed by Anotec is also included in Turbomeca LEDA software. The purpose is the same as the one above, but applied to broadband noise.
Ardiden 1H1 TEENI database
Tests realised in WP3 represent a very important database, with synchronised internal and external measurements, on the basis of which our knowledge of noise sources has been and will be challenged.
Already analysed in this project, data will be used again in the Record project to compare with calculations realised under the same conditions.
Decomposition methods applied by partners
Methods developed within WP2 and applied to full-scale engine test data enabled to build a first noise decomposition. This decomposition will act as a basis for analysing the whole Turbomeca database.
Anotec
Broadband noise decomposition tool
This method has been developed by Anotec within the above-mentioned LEDA tool developed by Turbomeca for analysing test data. Based on the broadband noise predictions from other TEENI tools it will enable a thorough treatment of the whole database, enabling a more precise update of semi-empirical methods for noise prediction.
Interface with Helena helicopter noise prediction platform
An interface was developed that makes it possible to use the results from the noise source decomposition, performed by LEDA, directly as input to the Helena helicopter noise prediction platform. This allows for a better assessment of the contribution of each engine noise source to the total helicopter noise and as such will assist in focussing efforts on reduction of the most relevant noise sources.
Avio
Method for broadband noise propagation through turbine rows
Within TEENI Avio has extended the existing tone noise analysis method to broadband noise propagation studies. This method is based on a time-linearised approach and assumes that the sound field generated by the interaction of a blade row with vortical and pressure disturbances coming from adjacent rows is a small perturbation of the background flow field. The extension proposed for the present investigation is based on the assumption that a broadband noise field can be seen as a superposition of an infinite number of uncorrelated modes, differing one another for the frequency value and /or the azimuthal and radial shape. These perturbations can be thus independently solved and finally summed together within the small perturbation hypothesis.
Systematic calculation of transmission /reflection coefficients
A significant amount of Civil Aviation Authority (CAA) simulations has been performed taking into account different turbine rows in order to calculate the acoustic response to selected incoming cut-on acoustic mode (circumferential as well as radial mode orders). Final result of this activity has been the calculation of transmission curves as a function of acoustic frequency and modal order. These curves work as transfer function and describe the acoustic interaction between the incoming wave and the row enabling the identification of correlation between the acoustic properties of the stator /rotor rows and the main geometric, aerodynamic and acoustic parameters (precious information in the early design phase).
Investigation on the applicability of quasi three-dimensional (Q3D) approximation
The introduction of the Q3D approximation (infinitesimal thickness duct) has been investigated as a way to reduce the computational time of the Bayesian belief network (BBN) propagation simulation. It turned out that this approximation gives sufficiently accurate results depending on the analysed frequency.
Bruël and Kjaër
Harmonic removal tools developed
A set of methods were developed to be able to solve the task of removing harmonic components from the time data recorded at the sensor positions. The output from the harmonic removal process constitutes broadband data to be further studied by noise source breakdown methods.
Blind source separation research
Research into blind source separation methodologies was conducted with the aim to pinpoint methods capable of solving the needs within the project. Several methods have been implemented based on already available code. The idea with the blind separation is to make the separation process simpler from a practical point of view.
Comoti
Sensor testing
Comoti carried out the experimental rig sensor testing for the microphone probes developed by DLR and the dielectric sensors developed by Inasco. The experimental program was aimed both at demonstrating that the new sensors can maintain structural integrity in the harsh environmental conditions (high temperature and pressure) to be expected in the hot region of a gas turbine engine and at providing reliable and accurate experimental data from independent measurement equipment, for the calibration of the new sensors.
The parallel measurements were carried out by means of temperature and pressure probes and particle image velocimetry and the database resulting from these experimental measurements forms a highly valuable foreground generated from the TEENI project. This database has already been used by two of Comoti's doctoral students for validation of their numerical works, in their respective theses and is expected to be further used for computational fluid dynamics (CFD) subroutines to be developed at Comoti, also as validation data. Two national research grant proposals on this subject are currently under evaluation.
Engine parts manufacturing
A second task Comoti was involved in was the manufacturing and design of new engine parts required for the adaptation of the helicopter engine used for final testing to the instrumentation required by the experimental program. The foreground generated by Comoti in this process was the optimisation of its manufacturing technologies, taking into account the high complexity of the parts that, due to the fact they were unique items, had to be manufactured from blocks, as no forged semi-finished parts existed, the budget and time constraints and the high strength, low manufacturability of the special materials required for the parts. The knowledge gained by Comoti in this activity will be further used for attracting and carrying out new design and manufacturing contracts, either economic, or in research grants.
DLR
High-pressure microphone probe
The newly developed microphone probe enables the assessment of acoustic pressure fluctuations up to an amplitude of 105 Pa even in harsh environment, i.e. at elevated pressure (up to 20bar above atmospheric pressure) and high temperature (e.g. in combustors with 1 200°C mean gas temperature). The probe can and will be used by the foreground owner (DLR) for acoustic investigations in model and full-scale aero engines where conventional instrumentation cannot be used. It will be also used in a dedicated hot-acoustic testrig of DLR for accurate assessment of acoustic dampers (so called liners) tested at elevated pressure and temperature. This testrig - together with the new probes - bridges the gap between commonly used cold-and-atmospheric investigations and the actual aero-engine application of these dampers, thereby adding valuable knowledge for the research community as well as validation data for the design tools of aero engine manufacturers.
Future investigations and development regarding this probe type will aim at better understanding of high pressure behaviour and also at reduced size and weight for even more simple installation in complex test setups.
New method for noise source discrimination
The new method for noise source discrimination will be used by the owner (DLR) for future research projects dealing with internal noise propagation in complex systems such as compressor and turbine stages. It is of great importance for better understanding the noise generation, propagation and specific effects such as frequency scattering or indirect combustion noise when the sound field is not easily accessible due to space and other constraints. With the findings of this analysis method it is possible to better distinguish between different noise sources present, weight their respective importance and adapt counter-measures (such as acoustic dampers) to the most relevant sources. Results of these research projects are frequently published at international conferences and journals, thereby adding to the knowledge of the scientific community.
EPFL
External sound source separation techniques
The enhanced acoustic goniometer is a specifically designed device, composed of geometrically arranged microphones ('array') to observe sound fields from a defined spatial solid angle. Here the design has been oriented towards focusing on the direct sound radiated by the turbine, excluding external noise contributions uncorrelated with the turbine. In addition to this array, it has been decided to use in parallel an octahedral array of six microphones.
The technique is based on the estimation of different time delay of arrival (TDOA) on several couples of microphones within the array, extrapolated to derive directions of arrival (DOA). The TDOA are estimated through inter-sensor cross-correlation estimation, using different weighting functions on the cross-correlation to enhance the accuracy.
Preliminary testing in anechoic conditions and for multiple sources have proven the capability of the array to simultaneously detect and localise multiple sound sources. The different post-processing techniques have been compared, leading to specification of the array (and processing) design with respect to the nature and number of the sound sources.
Microphone and sensor testing
In the frame of TEENI project, a novel test-rig has been specifically developed for the assessment of the performances of fluctuating temperature sensors (DLR). It is composed of a spinning perforated disc and of an acetylene flame welder combined to obtain 18 fluctuations of temperature per rotation. Finally the rotation per minute (RPM) control permits to modulate the frequency of temperature fluctuations. The number of RPM is manually regulated via an amplifier; the real RPM is measured using one external laser tachometer giving a pulse per rotation. The final frequency bandwidth obtained is 36 Hz to 900 Hz. At low frequency the disc is not cooled enough due to the high temperature flame (T>3 000°C), at high frequency some damage could appear on the whole mechanism due to induced vibrations.
Following recommendation of Microflown partner, one short wave tube (SWT) has been designed to make some qualification of the Microflown sensor. The SWT is composed of one acoustic driver connected to one rectangular steel tube with one access for the MF sensor and one for the reference microphone. Using this acoustic set-up, the calculation of the sensitivity of the sensor is done in the 100 Hz to 4 000 Hz bandwidth for sound pressure level up to 130 dB.
Inasco
Design of high temperature velocity fluctuation sensor
In the TEENI project a high temperature sensing element (based on dielectric measurement) for flow velocity fluctuations is developed. The sensor will be used in a gas turbine engine, at temperatures of around 650 °C and wind speeds of in excess of 200 m/s.
The sensor element consists of a durable substrate as insulator and metal/alloy as signal conductor. The substrate is used to support the positioning of two plates over its surface. The metal plates create the area of a capacitor and the engine gas is expected to flow within the plates. The metal plates are also used for the transportation of the signal away of the sensor surface.
In the particular sensor configuration, the metal plates are partly inserted in the ceramic substrate and they have an aerodynamic shape with flat active face. The sensor dimensions can be easily adapted according to project needs and dielectric measurement requirements.
The sensor operation consists in the creation of a homogeneous electric field (of constant intensity) between the metal plates. The gas flows in a direction perpendicular to the electric field lines in parallel to the sensor substrate surface.
The developed sensor has been tested at extreme conditions at the exhaust of a small turbojet engine where temperatures are above 800 °C without any problem. Sensor safety and performance testing took place in Comoti, where the feasibility was proven without any problem. The test plan for the dielectric sensors involved the progressive rise of the temperature in the sensor vicinity to the highest possible limit in order to test the survivability of the sensor in extreme environment. The maximum obtainable temperature for this engine was T=900 °C. The sensors appeared to perform equally well at this temperature level as well as afterwards. The velocity reached 130 m/sec. Visual inspection and examination of the sensors confirmed their excellent condition.
Microflown Technologies
Improved design of Microflown acoustic particle velocity sensor
A novel cleanroom design of the Microflown acoustic particle velocity sensor was developed that can operate at elevated temperatures up to 600 degrees Celsius, the wires themselves reaching around 750 °C. The work was subcontracted to the University of Twente.
A novel acoustic far field sound source localisation technique
A novel acoustic far field sound source localisation technique was developed capable of localising sound sources in a 3D space. Most of the work was done by an industry PhD, defending his thesis later in 2013 at the Institute of Sound and Vibration Research in Southampton.
Onera
Three sensors technique
This technique developed by Onera has been adapted in order to characterise the internal sources radiated during the full scale tests carried out with the Ardiden. It makes possible to extract the sound power levels of a source region measured locally by two sensors from the power spectral density measured by a microphone in far field. Moreover, the quality of the results can be assessed by comparing the deviation of the phase at the output of the method to the null phase.
TCD
Coherence-Based Noise-Source Identification Techniques
Both novel and existing methods of noise-source identification which apply the coherence function between pairs of in-engine microphones and far-field measurements have been tested for their suitability in full-scale engine tests using a small-scale experimental rig, before being applied using the data acquired for the full-scale Ardiden engine tests. Development of these techniques has allowed for better discrimination between the contributions of individual noise-sources within the engine (combustor, high-pressure turbine etc.) to the modal content of the noise radiated through the engine exhaust, as well as the noise radiated into the far-field. These techniques only require that a few reference sensors be located close to each noise-source of interest, which is beneficial for a real turboshaft engine where space is limited and the duct geometry is complex. More accurate identification of each noise-source's contribution to this measured noise has allowed for a better understanding to the generation and propagation of noise within the engine and therefore the possibility of enhanced mitigation through better informed acoustic liner design and location.
Scattering of Noise on Interaction with Rotating Turbomachinery
As noise propagates in turboshaft or similar aeroengines, this noise will interact with several rotor-stator stages. Both scattering on frequency (through a rotor) and mode order (through a rotor or stator) are possible under certain conditions linked to the characteristics of the incident noise and the rotor/stator geometries and rotational speeds. This frequency scattering phenomenon has not been the focus of an experimental study however. As part of the TEENI project, a small-scale test rig was designed to focus on this scattering of noise and found that both tonal and other noise can be scattered in this way, suggesting the possibility of frequency scattering and even spectral overlapping of broader-band scattered noise downstream of a compressor/turbine stage in a real engine.
Potential Impact:
Turbomeca
TEENI is part of the process of re-design of Turbomeca semi-empirical methods. These methods, designed from experimental results, are crucial for the engine manufacturer: they can estimate noise levels from the very beginning of a project, when very little information is available. TEENI has delivered elementary methods for engine noise test database treatment, on the basis of which the methods upgrade will be made possible. For the case where two different engines manufacturers are competing on a new product, confidence in forecasted acoustic levels is essential.
Through the identification of noise sources origin, we should be able to design better optimised liners for exhaust noise reduction and/or find ways to reduce noise at source.
Anotec
TEENI contributes to the continuous improvement of the Helena platform, managed by the Helena consortium, of which Turbomeca, Onera and Anotec are partners. This will finally contribute to an increased understanding of helicopter noise and thus enable further noise reduction.
TEENI results will be leveraged to the Soprano platform, Anotecs' fixed wing aircraft noise prediction platform, widely used in Europe. The noise source decomposition algorithm can be adapted so as to be used in the so-called static-to-inflight projection technique, often used as part of the noise certification process. This will allow Anotec to extend the range of certification services provided.
Avio
The control of the acoustic emissions is nowadays a critical aspect for the competitiveness of any aero-engine. Within TEENI Avio has developed a numerical method for broadband noise investigation and performed an extensive numerical work on aero-engine as well as turbo-shaft turbines, in order to investigate phenomena such as turbine shielding, modal and frequency scattering, while assessing the capability of the method to simulate broadband noise propagation in turbomachinery. This work results in a deeper comprehension of important acoustic aspects, revised design rules and, finally, a higher competitiveness for the Avio products.
Bruël and Kjaër
The blind source separation research conducted by Brüel and Kjaer during TEENI project is seen as platform towards more easy and practical methods for noise source investigations in the industry leading to pinpointing the cause of excessive noise levels. Based on this information noise level reduction improvements can be targeted.
Comoti
One of the strategic interests of Comoti is pursuing its increase in visibility and prestige at international level and the increase in scientific proficiency and technical expertise of its research staff. The project benefitted this strategic goal by allowing a significant contribution in a very complex and highly visible research field. Comoti's position in the European scientific community was consolidated by the dissemination of the results through scientific papers and participation in conferences, fairs and exhibitions, increasing its attractiveness for European and Romanian industrial or academic partners for future joint research projects. It also contributed to enhancing the proven expertise required for participating in European research projects, thus the potential of Romanian research to attract European funding. In support of this, Comoti's research team involved in TEENI had been awarded, as coordinator, two new FP7 research grants related to noise reduction and flame stability under supersonic conditions.
Furthermore, the experimental testing database resulting as foreground from this project is and will further be, used, in partnership with the "Politehnica" University of Bucharest and the Technical University of Iasi, as validation database for the numerical studies carried out by their students.
EPFL
The main research activity of EPFL in TEENI was devoted to the development/adaptation of the existing acoustic goniometer to the technical problem of turboshaft engine exhaust noise sources identification. The main scientific outcome was the achievement of an external compact microphone array to identify and separate multiple concurrent wideband sound sources in a confined configuration. Thus it can readily be considered as a significant contribution to noise source identification in several industrial fields where intrusive instrumentation is not possible or not accessible.
It is also worth mentioning that such techniques also apply to different other engineering fields and several have been already envisaged by EPFL that could have a significant societal impact. Among others:
1. road vehicle pass-by monitoring and tracking techniques, with capability of counting and estimating speed and size of vehicles along inter-city road (Marmaroli Patrick, 'Bimodal sound source tracking applied to road traffic monitoring', EPFL Thesis, n° 5618 (2013)). It could then serve as a deployable tool for monitoring noise pollution as well and collecting statistics on urban/inter-urban pollution.
2. microphone arrays for an unmanned aerial vehicle (UAV) to localise in real time concurrent UAVs for collision avoidance.
Inasco
With the successful implementation of the developed sensors Inasco will be able to expand its line of products to another market, this of the high temperature velocity and its fluctuation measurements. It is envisaged that within the next five years the high temperature sensors would be mature enough to be introduced to the market.
This is part of the company's long term strategy to introduce this technology to other fields of market, additional to the current one of composite manufacturing. Further to finished products like sensors and measurement systems, the knowledge and experience gained within TEENI will help in expanding company's service offerings, especially in the field of noise reduction technologies.
Microflown Technologies
The novel acoustic vector sensor based acoustic far field sound source localisation technique has been industrialised and is for instance used for the in flight monitoring of engines of larger (US) unmanned aerial platforms.
From 2012 till 2020, we expect to sell around 2 000 sensor nodes for EUR 20 000 each, so EUR 40 million turnover, gross margins 80 %.
There are clear ideas on how to bring the high temperature Microflown sensor element up to a technology readiness level of eight, but it will need quite some financial commitment.
Estimated research and development (R&D) is still 20 manyears, so around EUR 3 million.
Onera
The data based collected during TEENI project will allow new developments of data processing techniques, aiming at better understand the mechanisms at the origin of the noise generated inside an engine.
TCD
The analysis methods applied during the TEENI project (both existing techniques and novel methods) can be applied in a wide variety of duct acoustics scenarios where noise-source identification is being investigated, such as other types of aeroengine. The enhanced understanding of noise scattering developed as part of the project has resulted in the identification and prediction of a potential cause of tonal and broadband noise scattering in aeroengines, which may be erroneously attributed to other noise-sources when linear propagation path assumptions are made.
List of Websites:
http://www.xnoise.eu/about-x-noise/projects/generation-2-projects/teeni/summary/
