Final Report Summary - AFDAR (Advanced Flow Diagnostics for Aeronautical Research)
Executive Summary:
The objective of AFDAR is to develop, assess and demonstrate new image-based experimental technologies for the analysis of aerodynamic systems and aerospace propulsion components. The main development focus is on new three-dimensional methods based on Particle Image Velocimetry (PIV) to measure the flow field around aircraft components, and on the high-speed version of the planar technique for the analysis in time-resolved regime of transient/unsteady aerodynamic problems.
The progress beyond the state of the art with respect to current technologies is summarized by three aimed breakthroughs: 1) three-dimensional volumetric measurements over wings and airfoils; 2) time-resolved measurements and aerodynamic analysis several orders of magnitude faster than today; 3) turbulence characterization in aerodynamics wind-tunnels at resolution orders of magnitude higher than today by Long-Range Micro-PIV. The project ultimately aims to support the design of better aircraft and propulsion systems by enabling the designer to use experimental data during the development cycle of unprecedented completeness and quality. The work also covers the simultaneous application of PIV-based techniques and other methods to determine aero-acoustic noise emissions from airframe and to improve combustion processes to lower NOx, CO2 and soot emissions from engines.
The consortium is led by a Dutch Technical University and lists 10 partners including a Russian research Institute and an Australian University. Industries are involved in this work providing testing facilities. The project delivers a detailed analysis of the new measurement systems and a number of technology that validate these concepts in industrial environments.
The results are widely disseminated from small scale (consortium meetings, AFDAR workshops) to large scale (international symposia and conferences) and by scientific publications. A worldwide initiative to assess the state-of-the-art of PIV (www.pivchallenge.org) is initiated under AFDAR and will run beyond the time-frame and scope of the project.
Project Context and Objectives:
The objectives of the AFDAR project are intended to contribute within the wider scope and context of the EU efforts towards reaching a Greener and Sustainable Air Transport.
The need for radical improvements in the efficiency and reliability of air transportation has been clearly identified by the European commission in FP7 and through the launch of the Clean Sky Joint Technology Initiative. European aeronautics is committed to play a prime role in shaping aviation for this new age. Technological innovation and the development of better aeronautical systems require a significant effort in terms of upstream research to further extend the base of available technologies used in the development cycle of aircrafts.
In particular Europe seeks to build safer, greener and smarter aircraft and has agreed in 2007 on targets to cut greenhouse gas emissions by at least 20% until 2020. For that purpose, the objective is: to reduce fuel consumption and CO2 emissions by 50%; to reduce NOx emissions by 80% during landing and take-off. Last but not least, according to Europe strategic research agenda in aeronautics (ACARE), acoustic emissions should be reduced such to achieve 50% perceived external noise.
These objectives require significant improvements in the design of propulsion systems and external aerodynamics for the aeronautical industry, which in turn make necessary advanced verification tools for flow physics, including complex processes like combustion and aeroacoustics by means of experiments and computer simulations.
Development cycle innovation in aerospace
Despite of the impressive progress in the field of applied fluid mechanics and aerodynamics, the analysis and design of specific aircraft subsystems require more and more reliable approaches. This is particularly true when considering wings with high lift devices deployed or for the prediction and control of acoustic noise both from engines and from the airframe. Moreover the issue of NOx emissions is more commonly addressed downstream of the propulsion devices and breakthroughs may only be achieved if the flow processes occurring within the propulsion system are well understood by experimental visualizations in order to devise appropriate simulation schemes. It is therefore important to support the analysis of these specific configurations by appropriate diagnostic tools.
Beside the potential improvements in cruise flight drag, significant benefit can be expected from a better understanding of transient flight phases (e.g. take-off and landing). The high lift configurations often operate in presence of large flow separation where predictive models fail to return reliable estimates of the flow and detailed experiments are mandatory to validate CFD codes. As an example the activities performed in the EU FP6 C-WAKE and EU FP7 FAR-WAKE projects showed that advanced measurement techniques like PIV play a key role to understand and predict large transport aircraft vortex wakes. Moreover the overall efficiency of air transport relies heavily on modern propulsion systems. The improvement of jet engines is nowadays based on iterative aerodynamics and aerothermodynamics optimization of components such as compressor, combustor and turbine. These optimizations increasingly rely on the complete understanding of the complex interaction between primary and secondary flows present in these systems.
Image based flow diagnostics
Advanced experimental techniques provide improved physical knowledge of critical aerodynamic phenomena, in turn leading to better control strategies (e.g. improving performance of simpler designs such as single flap instead of double). It was clear already in FP6 that research programmes for the development of advanced flow diagnostics had a considerable impact in the innovation of aeronautical design processes. The last two decades have seen the exponential growth of image-based non-intrusive measurement techniques and in particular the development of digital particle image velocimetry (Willert and Gharib, 1991) sets a milestone in the area of flow diagnostics especially for experiments conducted in aeronautical wind-tunnels.
Given the high potential of this technique early European projects conducted in the 90s such EUROPIV and EUROPIV 2 have allowed to bring significant improvements to the PIV technique, but most importantly, to transfer PIV from the laboratory to realistic industrial application (Stanislas et al., 2000-2004). Subsequently the PIVNET and PIVNET 2 European thematic networks have enabled European researchers to establish world-wide leadership in the development and application of advanced concepts for flow measurements based on the Particle Image Velocimetry technique (Schroeder and Willert, 2008). As a result many European industries and laboratories support their R&D activities by the application state-of-the-art PIV during experimental verification of design concepts, resulting in improved competitiveness.
The central aim of the PIVNET II network (http://pivnet.dlr.de/ Schroeder and Willert, 2008) was to try to reduce the time to transfer PIV from the laboratory scale at research organizations, which pioneered various developments to a large variety of industrial applications. For that purpose, during the course of the network, a large variety of very successful workshops were organized around industrial demonstrations. Aside from targeting the field of aeronautics, other demonstrations focussed on turbomachinery, car aerodynamics, naval industry, household appliances, etc. Further special annual workshops were organized to foster contacts and cooperation between the major European PIV developers. Every other year this workshop took the form of an international PIV Challenge (benchmark of PIV evaluation algorithms, Stanislas et al., 2008), which demonstrated the strength of the European PIV community and its leading role worldwide in this field. These activities have been the background for the AFDAR project.
State of the art of PIV techniques and current limitations for industrial applications
One of the objectives in relation to the use of the above image-based flow diagnostics is that results obtained in the area of external aerodynamics achieved in the last 15 years by the very experts in the field, should now and in the future be realized by engineers of average expertise, in less time within industrial facilities. For instance the standard procedure to examine vortex dominated flows (aircrafts wing tip vortices, helicopters and propellers rotors) is based on experiments that make use of PIV, which have rapidly superseded previous methods based on probes or Laser Doppler Velocimetry.
The information obtained by experiments is of statistical nature meaning that ensemble or phase averaging is applied before the results are obtained. Dynamical events such a boundary layer transition, vortex breakdown or unsteady flow structure interaction could only seldom be described by experiments due to the scarce availability and low efficiency of high-speed illumination and recording systems at time.
The current capabilities of experimental methods are not capable of properly addressing a number of problems of high relevance for the industry. The points mentioned below constitute the main driver to perform the technological developments needed to progress beyond the state of the art.
- Understanding and predicting transient/unsteady phenomena: Reliable simulations of unsteady flow separation on aircraft wings, multi-element airfoils and powered engine nacelles at high Reynolds numbers still represent great challenges. The temporal motion of the separated region and the frequency and size of the shedding vortices must be known precisely for the validation of Unsteady Reynolds Averaged Simulations (URANS), Detached Eddy Simulations (DES) and Large Eddy Simulations (LES). At present, CCD technology and Nd:YAG lasers only allow to perform measurements at a typical rate of 5 to 15 Hz. In contrast the time scales involved in real flow conditions are in the order of 1000 Hz and higher. Therefore it is not possible, based on the above technology, to provide insights on the dynamical behaviour of aerodynamic flows of industrial relevance, for instance at the basis of structure vibration and acoustic noise production. So far, most experimental support to the development of CFD codes has been limited to statistical flow information (mean flow topology and averaged fluctuations).
- Analysis of small-scale turbulence: Despite the major advances performed in the last years in the area of turbulent flows simulation, a significant gap exists between the claimed potential of experimental techniques for the study of turbulent flow and what is really possible in industrial facilities. As a result, in industrial environment it is not common to perform detailed measurement of the flow turbulent structure. The main reason being the available spatial resolution, with typically a few millimetres size, fairly below that needed for high-Reynolds number flows, typical of industrial aerodynamics.
- Three-dimensional flows: In problems of practical interest, the flow exhibits three-dimensional behaviour. Above all turbulent flows always involve three dimensional motion, which can only be partly captured by the current planar PIV techniques. The dual-planar technique (Kaehler and Kompenhans, 2000) is an important step towards the measurement of 3D turbulent flows, but it remains limited to two adjacent planes. Phenomena such as transition, separation/reattachment and vortex dominated flows such as in propellers and turbomachinery require three-dimensional characterisation to fully support the validation of numerical techniques aiming at predicting the flow behaviour of these systems.
- Advances in combustion diagnostics: Combustion processes in aircraft engines require simultaneous determination of velocity, temperature and species concentration fields. Planar Laser Induced Fluorescence (PLIF) and Laser Induced Incandescence (LII) have been demonstrated to be suited to the task and separate experiments are possible at research laboratories such as those of DLR-K, CORIA and PC2A. It is however important to be able to establish the correlation between flow field and temperature and fuel concentration. The requirements for simultaneous PIV and PLIF measurements are at an early stage of development.
- Aero-acoustics and aero-elasticity: Velocity field measurements alone are not sufficient to solve the problems where flow induced vibrations (FIV) and aeroacoustics (AA) phenomena are of importance. The latter is highly relevant to the concerns raised about air traffic sustainable growth with the current level of acoustic emissions. Understanding and controlling aero-elastic behaviour has its relevance on safety when operating aircrafts in off-design conditions where flow separation and periodic vortex shedding may lead to amplification of structural vibrations. These regimes are not easily captured by current measurement techniques. PIV measurements do not follow these phenomena because of the low measurement rate. It is required that PIV measurements at high repetition rate are conducted simultaneously to surface pressure fluctuations and sound pressure level far away from the acoustic disturbance.
The objectives of the AFDAR proposal are a direct consequence of the above statements. The work starting point is the state-of-the-art of image based flow diagnostics laser techniques, which are well represented by the consortium participants. The aim is then to develop new concepts and procedures such to overcome the current limitations regarding measurement performances. The aim is not only to develop these new techniques per se but also to bring them to a level of technological readiness such that they can be usefully applied in contexts of industrial relevance. In this respect it has been essential that the partners of this project are excellent representatives of European research in this field, and each of them contributes with unique expertise and skills and specialized infrastructures.
AFDAR focal points and objectives
The AFDAR project focuses upon the following main topics, ranging from upstream research and development to industrial demonstrations:
a) Progress beyond the state of the art in PIV
- Extension to volume resolving (3D) flow field measurements (WP2)
- High frame-rate measurement in the kHz-rate for unsteady and transient phenomena (WP3)
- High resolution non-intrusive characterization of turbulent boundary layers and flow separation (WP3, WP5)
b) New application for aeronautical research
- Advanced diagnostics for the aerodynamics and aeroacoustics of high lift wing configurations (DNW-NWB is involved as subcontractor on these experiments, Model of “Community friendly aircraft” will be provided by research community around TU Braunschweig funded by German government) (WP5)
- High-resolution analysis of swept airfoil flow undergoing laminar separation and transition (WP5)
- High-resolution and 3D analysis of transonic turbine cascade (WP5)
- 3D analysis of an Ultra-Low NOx emissions combustor (AVIO collaborates providing the combustor prototype) (WP4)
- On-line high-speed diagnostics of helicopter rotor blade deformation and blade tip vortices velocity-density measurements (WP5)
c) Improvement of aircraft design tools and methodology
- Support to CFD validation by means of a specific benchmark on airfoil transition to turbulence
- Tools for visualization and exploration of experimental databases (WP4)
- Advances experimental methodologies for aeroacoustic analysis and aero-elastic verification (WP5)
Project Results:
S&T results contain many graphical material. This chapter is available through the a pdf file annexed to the project
Potential Impact:
The impact for AFDAR has been aimed at two activities of the work programme: 7.1.1 The greening of air transport; 7.1.4 Improving cost efficiency. In particular, the activities are pertinent to the sub areas “flight physics” (AAT.2010.1.1.1) and “propulsion” (AAT.2010.1.1.3). With the objective of reducing emissions addressed directly with the research on ultra-low NOx emission combustor and on the aeroacoustic analysis of wing profiles and flaps in high-lift configuration. Furthermore a potential impact is also achieved in the area of emission reduction considering the experimental means delivered that can study and optimize aerodynamic performances in off-design conditions and in high-lift configuration. Three main activities have focused on the development of advanced experimental analysis of engine subsystems: combustion diagnostics, three-dimensional aerodynamic analysis of combustor flows and a transonic turbine cascade.
The impact in flight physics is potentially achieved with the study of external aerodynamics of complex wing configurations (three-elements airfoil in high-lift). Such systems cannot yet be reliably predicted by CFD simulations especially in relation to the unsteady flow behaviour dominated by trailing vortices responsible of acoustic noise generation and unsteady aerodynamic loads. The experiments executed on this system can be used for reference when improving CFD software for the simulation of high lift systems.
Impact on “Improving Cost Efficiency” is achieved, considering the reduction of development costs achieved with the new experimental tools developed, in particular high-speed PIV supports the improvement of numerical tools for system design (AAT.2010.4.1.1. Design Systems and Tools).
More complete measurements of boundary layers, especially in adverse pressure gradient, wakes, tip and trailing vortices, improve the reliability of computer simulations by reducing the uncertainty for instance on turbulence closure models. The same considerations apply for the development of aero-engines where the experimental approaches demonstrated in AFDAR combine flow analysis and thermal and chemical species mapping, fundamental to the understanding and optimization of the combustion process.
The AFDAR project also aims at improving aircraft efficiency, by providing unprecedented details and insight in the 3D flow structure around wings and jet engine components. These results will evidently help designers to understand more deeply the flow around their prototypes and drive them to potential improvements. By a better quantitative assessment of flows such as vortices, wakes and boundary layers, both on the mean and instantaneous point of view, with a good spatial resolution and accuracy, the designer of wings, tails, bodies and engine nacelles of aircraft has now at hand an extensive experimental tool to push one step further the quality and safety of the aerodynamics of their products, for drag and noise reduction.
The activities performed in WP4 on the combination of advanced PIV techniques for the aeroacoustic analysis of wings and turbomachines have delivered experimental data bases of use for designers to improve the efficiency and reduce the aerodynamic noise sources.
The activities of AFDAR have brought an ideal cross link with the European Wind tunnels Association EWA in support of the generic activities on Measurement and Testing by providing new measurement technologies and supporting standardization and improvement of quality (WP5). By advertising the use of reference data bases in the form of high quality PIV recordings of standard flow conditions within an international framework of cooperation Europe and its industry potentially benefit from the AFDAR research and development.
The work conducted in AFDAR has much potential for aeronautics and wind tunnel operators (EWA). The European experts in the field have delivered through AFDAR the development of measurement techniques key for future aircraft development and wind tunnel characterization. Moreover, the AFDAR activities have been a unique opportunity not only to enable new types of measurements of higher quality and productivity, but they have also stimulated research teams from large research organizations such as DLR and CNRS to test and demonstrate their ability jointly, performing such complex measurement campaigns. Beside this operational aspect, the collaborative research effort has been of high scientific and technical level and can only be completed by the joint effort of most of the best research teams working in the field of PIV in Europe.
The formation of the consortium with the given partners organizations demonstrate the complementary and trans-national structure of the AFDAR consortium. A further impact of the project has been that of reinforcing the European competitiveness by leading edge joint research in the specific area of measurement technologies involving industry, ROR’s and universities around new promising experimental tools applied to targeted industrial objectives. The PIV research is oriented towards industrial applications and has been of precompetitive nature. The proposed project has provided synergies between different types of partners in three different directions:
developers ⇔ end users
aircraft aerodynamic technologies ⇔ propulsion technologies
developers and end users ⇔ manufacturers of PIV equipment.
Although the main contribution of the programme to the European Union policy has been of course in the transport field, by contributing to enhance the EU competitiveness in the field of air transport, considerable benefits can be translated to the sectors of ground transport, naval engineering and to some extent in all industrial fields that involve fluid dynamics.
AFDAR partners have actively cooperated in international organizations (Bi-annual Laser Symposium for Application of Laser Techniques to Fluid Mechanics in Lisbon and the International PIV Symposium, AIVELA, EREA partnership among few others).
Another added value of the AFDAR activities is that no individual company or university, nor any given European nation can afford to follow the different possible tracks to develop innovative PIV methods due to the costs it represents and the risks involved. The AFDAR activities thus are prototype of the kind of subject where cooperation at a European level offers benefits to all participants. Without the AFDAR project, it would have been unlikely for multilateral cooperation be continued. However, after having successfully performed cooperation during the work of AFDAR, the individual teams maintain research exchange and are placed in a good position to apply for international industrial projects, employing the newly developed PIV techniques.
Contribution to Community Social Objectives, Environment, health and safety
Being a research project with substantial upstream character AFDAR did not produce a direct impact on employment. Instead, its direct contribution was in improving the tools, skills and efficiency of European aeronautics industry, and indirectly AFDAR contributes to preserve employment in Europe. As far as the development of this method is concerned, the situation in Europe is unique. Similar initiatives have just started in Japan and do not exist in the US, which places Europe in at the forefront of this field.
Moreover, AFDAR achieved the unique goal of enhancing the general skill and knowledge available in Europe on this method. A large transfer of know how was done between the different countries and research organizations, making the method available at its best level for industry in more and more sites. This has been exchanged within AFDAR the use of advanced PIV systems in more complex flow fields was disseminated beyond the consortium. Participation of different European teams in joint presentations of the PIV technique, workshops, and working groups have stimulated transnational mobility.
The impact of AFDAR on employment as seen by the SMEs may be described by an example: LaVision, as manufacturer of PIV equipment, has four two persons for PIV during this project.
Also, nine teams from universities, research establishments from five European countries have contributed to the project. This is a direct mean to develop the knowledge of the research/teaching staff and to allow them to improve the education of their graduate students ‘on the job’ by providing first hand information about work in large industrial facilities and international projects.
Finally, several young scientists have grown to become responsible for some part of the research activities. This is also a unique opportunity to bring these young scientists at a high level of knowledge and skill, in a European environment. These will be available afterwards to strengthen industry and research organizations in their competition at international level.
In the field of environment, the contribution of the research activities of AFDAR may also be considered as indirect. It is by the contribution of the PIV method to the improvement of the performances of aircraft and the clear demonstration of such capabilities that AFDAR can contribute to the reduction of noise and pollution. Improvement of aerodynamic noise and reduction of fuel consumption will have a direct impact on the environment and preservation of natural resources and energy, as clearly stated in the fifth frame work program. Workshops and presentations dealing with multi-phase flows have also shown how their better understanding through application of PIV can optimise energy processes.
It is also by its help in making more efficient, less noisy and more safe aircraft, trains and cars that the newly developed PIV methods can be considered as contributing to the quality of life, comfort, health, mobility and safety of European citizens.
Economic Development
State-of-the-art PIV systems can be characterized as PIV systems which automate the data acquisition process by providing automatic system synchronisation and control hardware and software for all components for the system (lasers, CCD cameras, frame grabbers, computers, experiment). This makes the use of the PIV systems more straightforward. This is of practical significance particularly in industrial areas where there are high cost facilities, such as wind tunnels and engine test beds, and experimental time is constrained by tight development/production time schedules.
It is becoming a reality that more and more laboratories are making use of 3D PIV capabilities and in the next 10 years, it is most likely that the 3D-time resolved capabilities of the PIV technique will be used as an everyday measurement tool in almost all university, governmental and industrial research and development laboratories. AFDAR has played a primary role in fostering this development. Thus, the AFDAR project can be considered responsible for the further growth of market for advanced PIV systems, for the understanding of the basic principles, advantages and limitations of the method, and for training in the application of PIV to measure flow fields. This directly impacts the market prospects as seen by those SMEs manufacturing PIV equipment.
As clear from the description of individual consortium partners, the existing knowledge, expertise and skills in the field of particle image velocimetry techniques were excellently represented by AFDAR participants. This condition has enabled performing activities at the edge of current state-of-the-art for spreading of excellence.
The first mean to spread excellence has been mobilizing researchers among the consortium participants, which enabled further strengthening of the competences and multi-disciplinary skills within the consortium. This is the result of the large number of collaboration activities involved with the AFDAR tasks mostly performed jointly by two to three partners.
The second step has been to organize specific workshops where personnel not belonging to the consortium has been able to follow introductory lectures and practical laboratory activities familiarizing with the peculiar aspects of tomographic PIV, high-speed measurements and combined optical measurement techniques.
The dissemination at broadest level has been performed by specific actions:
i) a VKI Lecture Series coordinated by AFDAR partners on the post-processing of experimental and numerical data
ii) The DLR PIV course has served as a yearly event to revise the state of the art of the techniques under development in AFDAR. It should be known that this course has now achieved a large impact in the scientific and industrial community and the number of people attending it has steadily grown over the years
iii) All the consortium participants have a rather conspicuous scientific productivity and most results have been disseminated directly by peer-reviewed publications on international journals. The close relation between some of the consortium members and editorial boards of experimental fluid mechanics and measurement techniques journals resulted in a special issue on the developments from a number of AFDAR partners
iv) Progress meetings have been connected with major events (Lisbon Conference on the Applications of Laser Techniques to Fluid Mechanics, Biannual International Symposium on Particle Image Velocimetry) and when possible open to non AFDAR participants to maximize the dissemination of results. This formula has been already adopted for other European projects like PIVNET and turned out to be successful to the point that the workshops had an impact comparable to that of the major conference.
List of Websites:
The address of the project public website is: http://afdar.eu
The contact information can be found on the AFDAR website: http://www.afdar.eu/contact
For information on the AFDAR project, please contact:
Scientific Coordinator Project Management
Prof. Dr. Fulvio Scarano
Head of AWEP Department
TU Delft / Faculty of Aerospace Engineering
Building 62
Kluyverweg 1
2629 HS Delft
T +31 (0)15 27 85902
E f.scarano@tudelft.nl
Dr. Ni Yan
Project Manager European Collaboration
TU Delft / Valorisation Centre (VC)
Building 36
Mekelweg 4
2628 CD Delft
T +31 (0)15 27 83059
E n.yan@tudelft.nl
For questions regarding the AFDAR project website, please contact:
Mr. Alwin Wink
TU Delft / Valorisation Centre (VC)
Building 36
Mekelweg 4
2628 CD Delft
T +31 (0)15 2784233
F +31 (0)15 2781179
E a.d.wink@tudelft.nl
The objective of AFDAR is to develop, assess and demonstrate new image-based experimental technologies for the analysis of aerodynamic systems and aerospace propulsion components. The main development focus is on new three-dimensional methods based on Particle Image Velocimetry (PIV) to measure the flow field around aircraft components, and on the high-speed version of the planar technique for the analysis in time-resolved regime of transient/unsteady aerodynamic problems.
The progress beyond the state of the art with respect to current technologies is summarized by three aimed breakthroughs: 1) three-dimensional volumetric measurements over wings and airfoils; 2) time-resolved measurements and aerodynamic analysis several orders of magnitude faster than today; 3) turbulence characterization in aerodynamics wind-tunnels at resolution orders of magnitude higher than today by Long-Range Micro-PIV. The project ultimately aims to support the design of better aircraft and propulsion systems by enabling the designer to use experimental data during the development cycle of unprecedented completeness and quality. The work also covers the simultaneous application of PIV-based techniques and other methods to determine aero-acoustic noise emissions from airframe and to improve combustion processes to lower NOx, CO2 and soot emissions from engines.
The consortium is led by a Dutch Technical University and lists 10 partners including a Russian research Institute and an Australian University. Industries are involved in this work providing testing facilities. The project delivers a detailed analysis of the new measurement systems and a number of technology that validate these concepts in industrial environments.
The results are widely disseminated from small scale (consortium meetings, AFDAR workshops) to large scale (international symposia and conferences) and by scientific publications. A worldwide initiative to assess the state-of-the-art of PIV (www.pivchallenge.org) is initiated under AFDAR and will run beyond the time-frame and scope of the project.
Project Context and Objectives:
The objectives of the AFDAR project are intended to contribute within the wider scope and context of the EU efforts towards reaching a Greener and Sustainable Air Transport.
The need for radical improvements in the efficiency and reliability of air transportation has been clearly identified by the European commission in FP7 and through the launch of the Clean Sky Joint Technology Initiative. European aeronautics is committed to play a prime role in shaping aviation for this new age. Technological innovation and the development of better aeronautical systems require a significant effort in terms of upstream research to further extend the base of available technologies used in the development cycle of aircrafts.
In particular Europe seeks to build safer, greener and smarter aircraft and has agreed in 2007 on targets to cut greenhouse gas emissions by at least 20% until 2020. For that purpose, the objective is: to reduce fuel consumption and CO2 emissions by 50%; to reduce NOx emissions by 80% during landing and take-off. Last but not least, according to Europe strategic research agenda in aeronautics (ACARE), acoustic emissions should be reduced such to achieve 50% perceived external noise.
These objectives require significant improvements in the design of propulsion systems and external aerodynamics for the aeronautical industry, which in turn make necessary advanced verification tools for flow physics, including complex processes like combustion and aeroacoustics by means of experiments and computer simulations.
Development cycle innovation in aerospace
Despite of the impressive progress in the field of applied fluid mechanics and aerodynamics, the analysis and design of specific aircraft subsystems require more and more reliable approaches. This is particularly true when considering wings with high lift devices deployed or for the prediction and control of acoustic noise both from engines and from the airframe. Moreover the issue of NOx emissions is more commonly addressed downstream of the propulsion devices and breakthroughs may only be achieved if the flow processes occurring within the propulsion system are well understood by experimental visualizations in order to devise appropriate simulation schemes. It is therefore important to support the analysis of these specific configurations by appropriate diagnostic tools.
Beside the potential improvements in cruise flight drag, significant benefit can be expected from a better understanding of transient flight phases (e.g. take-off and landing). The high lift configurations often operate in presence of large flow separation where predictive models fail to return reliable estimates of the flow and detailed experiments are mandatory to validate CFD codes. As an example the activities performed in the EU FP6 C-WAKE and EU FP7 FAR-WAKE projects showed that advanced measurement techniques like PIV play a key role to understand and predict large transport aircraft vortex wakes. Moreover the overall efficiency of air transport relies heavily on modern propulsion systems. The improvement of jet engines is nowadays based on iterative aerodynamics and aerothermodynamics optimization of components such as compressor, combustor and turbine. These optimizations increasingly rely on the complete understanding of the complex interaction between primary and secondary flows present in these systems.
Image based flow diagnostics
Advanced experimental techniques provide improved physical knowledge of critical aerodynamic phenomena, in turn leading to better control strategies (e.g. improving performance of simpler designs such as single flap instead of double). It was clear already in FP6 that research programmes for the development of advanced flow diagnostics had a considerable impact in the innovation of aeronautical design processes. The last two decades have seen the exponential growth of image-based non-intrusive measurement techniques and in particular the development of digital particle image velocimetry (Willert and Gharib, 1991) sets a milestone in the area of flow diagnostics especially for experiments conducted in aeronautical wind-tunnels.
Given the high potential of this technique early European projects conducted in the 90s such EUROPIV and EUROPIV 2 have allowed to bring significant improvements to the PIV technique, but most importantly, to transfer PIV from the laboratory to realistic industrial application (Stanislas et al., 2000-2004). Subsequently the PIVNET and PIVNET 2 European thematic networks have enabled European researchers to establish world-wide leadership in the development and application of advanced concepts for flow measurements based on the Particle Image Velocimetry technique (Schroeder and Willert, 2008). As a result many European industries and laboratories support their R&D activities by the application state-of-the-art PIV during experimental verification of design concepts, resulting in improved competitiveness.
The central aim of the PIVNET II network (http://pivnet.dlr.de/ Schroeder and Willert, 2008) was to try to reduce the time to transfer PIV from the laboratory scale at research organizations, which pioneered various developments to a large variety of industrial applications. For that purpose, during the course of the network, a large variety of very successful workshops were organized around industrial demonstrations. Aside from targeting the field of aeronautics, other demonstrations focussed on turbomachinery, car aerodynamics, naval industry, household appliances, etc. Further special annual workshops were organized to foster contacts and cooperation between the major European PIV developers. Every other year this workshop took the form of an international PIV Challenge (benchmark of PIV evaluation algorithms, Stanislas et al., 2008), which demonstrated the strength of the European PIV community and its leading role worldwide in this field. These activities have been the background for the AFDAR project.
State of the art of PIV techniques and current limitations for industrial applications
One of the objectives in relation to the use of the above image-based flow diagnostics is that results obtained in the area of external aerodynamics achieved in the last 15 years by the very experts in the field, should now and in the future be realized by engineers of average expertise, in less time within industrial facilities. For instance the standard procedure to examine vortex dominated flows (aircrafts wing tip vortices, helicopters and propellers rotors) is based on experiments that make use of PIV, which have rapidly superseded previous methods based on probes or Laser Doppler Velocimetry.
The information obtained by experiments is of statistical nature meaning that ensemble or phase averaging is applied before the results are obtained. Dynamical events such a boundary layer transition, vortex breakdown or unsteady flow structure interaction could only seldom be described by experiments due to the scarce availability and low efficiency of high-speed illumination and recording systems at time.
The current capabilities of experimental methods are not capable of properly addressing a number of problems of high relevance for the industry. The points mentioned below constitute the main driver to perform the technological developments needed to progress beyond the state of the art.
- Understanding and predicting transient/unsteady phenomena: Reliable simulations of unsteady flow separation on aircraft wings, multi-element airfoils and powered engine nacelles at high Reynolds numbers still represent great challenges. The temporal motion of the separated region and the frequency and size of the shedding vortices must be known precisely for the validation of Unsteady Reynolds Averaged Simulations (URANS), Detached Eddy Simulations (DES) and Large Eddy Simulations (LES). At present, CCD technology and Nd:YAG lasers only allow to perform measurements at a typical rate of 5 to 15 Hz. In contrast the time scales involved in real flow conditions are in the order of 1000 Hz and higher. Therefore it is not possible, based on the above technology, to provide insights on the dynamical behaviour of aerodynamic flows of industrial relevance, for instance at the basis of structure vibration and acoustic noise production. So far, most experimental support to the development of CFD codes has been limited to statistical flow information (mean flow topology and averaged fluctuations).
- Analysis of small-scale turbulence: Despite the major advances performed in the last years in the area of turbulent flows simulation, a significant gap exists between the claimed potential of experimental techniques for the study of turbulent flow and what is really possible in industrial facilities. As a result, in industrial environment it is not common to perform detailed measurement of the flow turbulent structure. The main reason being the available spatial resolution, with typically a few millimetres size, fairly below that needed for high-Reynolds number flows, typical of industrial aerodynamics.
- Three-dimensional flows: In problems of practical interest, the flow exhibits three-dimensional behaviour. Above all turbulent flows always involve three dimensional motion, which can only be partly captured by the current planar PIV techniques. The dual-planar technique (Kaehler and Kompenhans, 2000) is an important step towards the measurement of 3D turbulent flows, but it remains limited to two adjacent planes. Phenomena such as transition, separation/reattachment and vortex dominated flows such as in propellers and turbomachinery require three-dimensional characterisation to fully support the validation of numerical techniques aiming at predicting the flow behaviour of these systems.
- Advances in combustion diagnostics: Combustion processes in aircraft engines require simultaneous determination of velocity, temperature and species concentration fields. Planar Laser Induced Fluorescence (PLIF) and Laser Induced Incandescence (LII) have been demonstrated to be suited to the task and separate experiments are possible at research laboratories such as those of DLR-K, CORIA and PC2A. It is however important to be able to establish the correlation between flow field and temperature and fuel concentration. The requirements for simultaneous PIV and PLIF measurements are at an early stage of development.
- Aero-acoustics and aero-elasticity: Velocity field measurements alone are not sufficient to solve the problems where flow induced vibrations (FIV) and aeroacoustics (AA) phenomena are of importance. The latter is highly relevant to the concerns raised about air traffic sustainable growth with the current level of acoustic emissions. Understanding and controlling aero-elastic behaviour has its relevance on safety when operating aircrafts in off-design conditions where flow separation and periodic vortex shedding may lead to amplification of structural vibrations. These regimes are not easily captured by current measurement techniques. PIV measurements do not follow these phenomena because of the low measurement rate. It is required that PIV measurements at high repetition rate are conducted simultaneously to surface pressure fluctuations and sound pressure level far away from the acoustic disturbance.
The objectives of the AFDAR proposal are a direct consequence of the above statements. The work starting point is the state-of-the-art of image based flow diagnostics laser techniques, which are well represented by the consortium participants. The aim is then to develop new concepts and procedures such to overcome the current limitations regarding measurement performances. The aim is not only to develop these new techniques per se but also to bring them to a level of technological readiness such that they can be usefully applied in contexts of industrial relevance. In this respect it has been essential that the partners of this project are excellent representatives of European research in this field, and each of them contributes with unique expertise and skills and specialized infrastructures.
AFDAR focal points and objectives
The AFDAR project focuses upon the following main topics, ranging from upstream research and development to industrial demonstrations:
a) Progress beyond the state of the art in PIV
- Extension to volume resolving (3D) flow field measurements (WP2)
- High frame-rate measurement in the kHz-rate for unsteady and transient phenomena (WP3)
- High resolution non-intrusive characterization of turbulent boundary layers and flow separation (WP3, WP5)
b) New application for aeronautical research
- Advanced diagnostics for the aerodynamics and aeroacoustics of high lift wing configurations (DNW-NWB is involved as subcontractor on these experiments, Model of “Community friendly aircraft” will be provided by research community around TU Braunschweig funded by German government) (WP5)
- High-resolution analysis of swept airfoil flow undergoing laminar separation and transition (WP5)
- High-resolution and 3D analysis of transonic turbine cascade (WP5)
- 3D analysis of an Ultra-Low NOx emissions combustor (AVIO collaborates providing the combustor prototype) (WP4)
- On-line high-speed diagnostics of helicopter rotor blade deformation and blade tip vortices velocity-density measurements (WP5)
c) Improvement of aircraft design tools and methodology
- Support to CFD validation by means of a specific benchmark on airfoil transition to turbulence
- Tools for visualization and exploration of experimental databases (WP4)
- Advances experimental methodologies for aeroacoustic analysis and aero-elastic verification (WP5)
Project Results:
S&T results contain many graphical material. This chapter is available through the a pdf file annexed to the project
Potential Impact:
The impact for AFDAR has been aimed at two activities of the work programme: 7.1.1 The greening of air transport; 7.1.4 Improving cost efficiency. In particular, the activities are pertinent to the sub areas “flight physics” (AAT.2010.1.1.1) and “propulsion” (AAT.2010.1.1.3). With the objective of reducing emissions addressed directly with the research on ultra-low NOx emission combustor and on the aeroacoustic analysis of wing profiles and flaps in high-lift configuration. Furthermore a potential impact is also achieved in the area of emission reduction considering the experimental means delivered that can study and optimize aerodynamic performances in off-design conditions and in high-lift configuration. Three main activities have focused on the development of advanced experimental analysis of engine subsystems: combustion diagnostics, three-dimensional aerodynamic analysis of combustor flows and a transonic turbine cascade.
The impact in flight physics is potentially achieved with the study of external aerodynamics of complex wing configurations (three-elements airfoil in high-lift). Such systems cannot yet be reliably predicted by CFD simulations especially in relation to the unsteady flow behaviour dominated by trailing vortices responsible of acoustic noise generation and unsteady aerodynamic loads. The experiments executed on this system can be used for reference when improving CFD software for the simulation of high lift systems.
Impact on “Improving Cost Efficiency” is achieved, considering the reduction of development costs achieved with the new experimental tools developed, in particular high-speed PIV supports the improvement of numerical tools for system design (AAT.2010.4.1.1. Design Systems and Tools).
More complete measurements of boundary layers, especially in adverse pressure gradient, wakes, tip and trailing vortices, improve the reliability of computer simulations by reducing the uncertainty for instance on turbulence closure models. The same considerations apply for the development of aero-engines where the experimental approaches demonstrated in AFDAR combine flow analysis and thermal and chemical species mapping, fundamental to the understanding and optimization of the combustion process.
The AFDAR project also aims at improving aircraft efficiency, by providing unprecedented details and insight in the 3D flow structure around wings and jet engine components. These results will evidently help designers to understand more deeply the flow around their prototypes and drive them to potential improvements. By a better quantitative assessment of flows such as vortices, wakes and boundary layers, both on the mean and instantaneous point of view, with a good spatial resolution and accuracy, the designer of wings, tails, bodies and engine nacelles of aircraft has now at hand an extensive experimental tool to push one step further the quality and safety of the aerodynamics of their products, for drag and noise reduction.
The activities performed in WP4 on the combination of advanced PIV techniques for the aeroacoustic analysis of wings and turbomachines have delivered experimental data bases of use for designers to improve the efficiency and reduce the aerodynamic noise sources.
The activities of AFDAR have brought an ideal cross link with the European Wind tunnels Association EWA in support of the generic activities on Measurement and Testing by providing new measurement technologies and supporting standardization and improvement of quality (WP5). By advertising the use of reference data bases in the form of high quality PIV recordings of standard flow conditions within an international framework of cooperation Europe and its industry potentially benefit from the AFDAR research and development.
The work conducted in AFDAR has much potential for aeronautics and wind tunnel operators (EWA). The European experts in the field have delivered through AFDAR the development of measurement techniques key for future aircraft development and wind tunnel characterization. Moreover, the AFDAR activities have been a unique opportunity not only to enable new types of measurements of higher quality and productivity, but they have also stimulated research teams from large research organizations such as DLR and CNRS to test and demonstrate their ability jointly, performing such complex measurement campaigns. Beside this operational aspect, the collaborative research effort has been of high scientific and technical level and can only be completed by the joint effort of most of the best research teams working in the field of PIV in Europe.
The formation of the consortium with the given partners organizations demonstrate the complementary and trans-national structure of the AFDAR consortium. A further impact of the project has been that of reinforcing the European competitiveness by leading edge joint research in the specific area of measurement technologies involving industry, ROR’s and universities around new promising experimental tools applied to targeted industrial objectives. The PIV research is oriented towards industrial applications and has been of precompetitive nature. The proposed project has provided synergies between different types of partners in three different directions:
developers ⇔ end users
aircraft aerodynamic technologies ⇔ propulsion technologies
developers and end users ⇔ manufacturers of PIV equipment.
Although the main contribution of the programme to the European Union policy has been of course in the transport field, by contributing to enhance the EU competitiveness in the field of air transport, considerable benefits can be translated to the sectors of ground transport, naval engineering and to some extent in all industrial fields that involve fluid dynamics.
AFDAR partners have actively cooperated in international organizations (Bi-annual Laser Symposium for Application of Laser Techniques to Fluid Mechanics in Lisbon and the International PIV Symposium, AIVELA, EREA partnership among few others).
Another added value of the AFDAR activities is that no individual company or university, nor any given European nation can afford to follow the different possible tracks to develop innovative PIV methods due to the costs it represents and the risks involved. The AFDAR activities thus are prototype of the kind of subject where cooperation at a European level offers benefits to all participants. Without the AFDAR project, it would have been unlikely for multilateral cooperation be continued. However, after having successfully performed cooperation during the work of AFDAR, the individual teams maintain research exchange and are placed in a good position to apply for international industrial projects, employing the newly developed PIV techniques.
Contribution to Community Social Objectives, Environment, health and safety
Being a research project with substantial upstream character AFDAR did not produce a direct impact on employment. Instead, its direct contribution was in improving the tools, skills and efficiency of European aeronautics industry, and indirectly AFDAR contributes to preserve employment in Europe. As far as the development of this method is concerned, the situation in Europe is unique. Similar initiatives have just started in Japan and do not exist in the US, which places Europe in at the forefront of this field.
Moreover, AFDAR achieved the unique goal of enhancing the general skill and knowledge available in Europe on this method. A large transfer of know how was done between the different countries and research organizations, making the method available at its best level for industry in more and more sites. This has been exchanged within AFDAR the use of advanced PIV systems in more complex flow fields was disseminated beyond the consortium. Participation of different European teams in joint presentations of the PIV technique, workshops, and working groups have stimulated transnational mobility.
The impact of AFDAR on employment as seen by the SMEs may be described by an example: LaVision, as manufacturer of PIV equipment, has four two persons for PIV during this project.
Also, nine teams from universities, research establishments from five European countries have contributed to the project. This is a direct mean to develop the knowledge of the research/teaching staff and to allow them to improve the education of their graduate students ‘on the job’ by providing first hand information about work in large industrial facilities and international projects.
Finally, several young scientists have grown to become responsible for some part of the research activities. This is also a unique opportunity to bring these young scientists at a high level of knowledge and skill, in a European environment. These will be available afterwards to strengthen industry and research organizations in their competition at international level.
In the field of environment, the contribution of the research activities of AFDAR may also be considered as indirect. It is by the contribution of the PIV method to the improvement of the performances of aircraft and the clear demonstration of such capabilities that AFDAR can contribute to the reduction of noise and pollution. Improvement of aerodynamic noise and reduction of fuel consumption will have a direct impact on the environment and preservation of natural resources and energy, as clearly stated in the fifth frame work program. Workshops and presentations dealing with multi-phase flows have also shown how their better understanding through application of PIV can optimise energy processes.
It is also by its help in making more efficient, less noisy and more safe aircraft, trains and cars that the newly developed PIV methods can be considered as contributing to the quality of life, comfort, health, mobility and safety of European citizens.
Economic Development
State-of-the-art PIV systems can be characterized as PIV systems which automate the data acquisition process by providing automatic system synchronisation and control hardware and software for all components for the system (lasers, CCD cameras, frame grabbers, computers, experiment). This makes the use of the PIV systems more straightforward. This is of practical significance particularly in industrial areas where there are high cost facilities, such as wind tunnels and engine test beds, and experimental time is constrained by tight development/production time schedules.
It is becoming a reality that more and more laboratories are making use of 3D PIV capabilities and in the next 10 years, it is most likely that the 3D-time resolved capabilities of the PIV technique will be used as an everyday measurement tool in almost all university, governmental and industrial research and development laboratories. AFDAR has played a primary role in fostering this development. Thus, the AFDAR project can be considered responsible for the further growth of market for advanced PIV systems, for the understanding of the basic principles, advantages and limitations of the method, and for training in the application of PIV to measure flow fields. This directly impacts the market prospects as seen by those SMEs manufacturing PIV equipment.
As clear from the description of individual consortium partners, the existing knowledge, expertise and skills in the field of particle image velocimetry techniques were excellently represented by AFDAR participants. This condition has enabled performing activities at the edge of current state-of-the-art for spreading of excellence.
The first mean to spread excellence has been mobilizing researchers among the consortium participants, which enabled further strengthening of the competences and multi-disciplinary skills within the consortium. This is the result of the large number of collaboration activities involved with the AFDAR tasks mostly performed jointly by two to three partners.
The second step has been to organize specific workshops where personnel not belonging to the consortium has been able to follow introductory lectures and practical laboratory activities familiarizing with the peculiar aspects of tomographic PIV, high-speed measurements and combined optical measurement techniques.
The dissemination at broadest level has been performed by specific actions:
i) a VKI Lecture Series coordinated by AFDAR partners on the post-processing of experimental and numerical data
ii) The DLR PIV course has served as a yearly event to revise the state of the art of the techniques under development in AFDAR. It should be known that this course has now achieved a large impact in the scientific and industrial community and the number of people attending it has steadily grown over the years
iii) All the consortium participants have a rather conspicuous scientific productivity and most results have been disseminated directly by peer-reviewed publications on international journals. The close relation between some of the consortium members and editorial boards of experimental fluid mechanics and measurement techniques journals resulted in a special issue on the developments from a number of AFDAR partners
iv) Progress meetings have been connected with major events (Lisbon Conference on the Applications of Laser Techniques to Fluid Mechanics, Biannual International Symposium on Particle Image Velocimetry) and when possible open to non AFDAR participants to maximize the dissemination of results. This formula has been already adopted for other European projects like PIVNET and turned out to be successful to the point that the workshops had an impact comparable to that of the major conference.
List of Websites:
The address of the project public website is: http://afdar.eu
The contact information can be found on the AFDAR website: http://www.afdar.eu/contact
For information on the AFDAR project, please contact:
Scientific Coordinator Project Management
Prof. Dr. Fulvio Scarano
Head of AWEP Department
TU Delft / Faculty of Aerospace Engineering
Building 62
Kluyverweg 1
2629 HS Delft
T +31 (0)15 27 85902
E f.scarano@tudelft.nl
Dr. Ni Yan
Project Manager European Collaboration
TU Delft / Valorisation Centre (VC)
Building 36
Mekelweg 4
2628 CD Delft
T +31 (0)15 27 83059
E n.yan@tudelft.nl
For questions regarding the AFDAR project website, please contact:
Mr. Alwin Wink
TU Delft / Valorisation Centre (VC)
Building 36
Mekelweg 4
2628 CD Delft
T +31 (0)15 2784233
F +31 (0)15 2781179
E a.d.wink@tudelft.nl
