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Useful PLASMa for AEROdynamic control

Final Report Summary - PLASMAERO (Useful plasma for aerodynamic control)

Executive summary:

This document gives an overview of the European PLASMAERO project which lasted 39 months between 1 October 2009 and 31 December 2012. It presents the context, the consortium and the objectives of the project. It describes the results of the most promising plasma actuators to control or improve the flow of the chosen aerodynamic configurations, subsonic, transonic and in atmospheric conditions and supplies the assessment of the project.

It synthesises all the numerical and experimental works performed in the PLASMAERO project and analyses the results of the plasma actuators operation and their effect on flow control. It provides the main recommendations for future works on plasmas actuators conception and on protocol for flow control by plasmas.

Project context and objectives:

PLASMAERO is a Seventh Framework Programme (FP7) collaborative research project led by ONERA seeking to demonstrate how surface and arc discharge plasma actuators can be used to influence and control aircraft flows.

The design of tomorrow's aircraft will be dictated by the need to have more environmentally 'green' aircraft in line with the 'ACARE Vision 2020'. Optimised aerodynamic performance can be one way to achieve this.

With the continued objective of increasing aircraft performances whilst reducing the environmental impact, research is being carried out to find innovative solutions to influence air flow using simple actuators. If the aerodynamic configuration of future aircraft could be modified in real time in flight, then the aircraft's performance could be continually adapted to provide optimum aerodynamic characteristics.

Amongst the innovative solutions, the use of plasma technologies has shown itself to be very promising from both a performance point of view and in terms of the diversity in potential applications such as external and internal flow control, combustion enhancement and noise attenuation.

The main advantages of plasmas devices are their easy manufacturing, integration simplicity and ability for real time control at high frequency. There are no moving parts and only two thin electrical wires connected to their electrical power.

To move forward towards this objective, it is necessary to study breakthrough emerging technologies going beyond the limitations of the aircraft's fixed structure and to use efficient actuators to optimise the flow status over the airfoil.

PLASMAERO sought to demonstrate how dielectric barrier discharge (DBD) and spark-discharge plasma actuators could be used to control aircraft aerodynamic flows. This was achieved through an enhanced understanding of their physical characteristics and an in-depth study of how they may be optimised to influence the air flow properties. More specifically, the project objectives were to:

- understand, model and classify, through experimental and numerical studies, the most relevant physical characteristics plasma actuators capable of influencing airflow;
- perform comparative experimental tests and numerical studies of different actuator configurations to select the most promising features for further development;
- demonstrate through wind tunnel experimentations the ability of plasma devices to significantly improve the aerodynamics in terms of lift, lift / drag and high lift noise in representative aeronautical airflow conditions (take-off, cruise and landing);
- demonstrate the ease of use and installation of these actuators in a reduced size flight platform;
- provide exhaustive recommendations on future work to achieve the implementation of this technological baseline on next generation aircraft programmes.

11 partners from 7 countries are involved in PLASMAERO (please note that the list of partners and their main points of contact is attached in SESAM as a PDF file).

ONERA coordinates the project, which is broken down into 6 work packages (WPs):

- 4 research and technology development (RTD) (WPs 1 to 4);
- 1 dissemination (WP5);
- 1 management (WP0)

RTD:

WP1: Plasma device investigation, development, manufacturing and improvement (leader: EPFL)

- further understand the physics of plasmas with and without flow;
- improve, design, development and manufacture the plasma actuators (devices) needed to respond to the requirements of the defined aerodynamic configuration.

WP2: Physics modelling and computation (leader: CNRS)

- modelling the plasma physics of the actuators;
- coupling the plasma solver to aerodynamic codes;
- application to aerodynamic configurations to define the possibilities of flow control.

WP3: Wind tunnel investigations for flow control (leader: ONERA)

- demonstrate the feasibility of using plasma actuators to be used in real aerodynamic configurations (two-dimensional (2D), 3D, subsonic and transonic flows).

WP4: Validation and integration (leader: TUD)

- validate selected plasma actuators in realistic aerodynamic configurations (2D and 3D, subsonic and transonic flows in wind tunnels);
- develop a small scale fully integrated demonstrator as an outlook on the easy and effective applicability of the flow-control devices developed in this project on full size flight vehicles.

Dissemination:

WP5: Dissemination, exploitation and training (leader: ONERA)

- make aware the European academia and industry of the project;
- communicate within Europe results and potential impact of project results.

Management:

WP0: Consortium management (leader: ONERA)

- set up the management infrastructure (committees, boards, quality plan, procedures, risk, registers, project management tools, internal website, etc);
- provide technical coordination of the project partners;
- provide financial and contractual management of the consortium, including maintenance of the consortium agreement and intellectual property right (IPR) issues.

Project results:

This section summarises and synthesises the numerical and experimental results obtained from the project. The analysis of the operation of plasmas actuators and their effect on flow control are also described. A project assessment including recommendations for future work is given at the end. The research subjects include:

- design and development of plasmas actuators:
a) different DBD using ionic wind -> single, multi, VG, floating;
b) nanosecond DBD using pressure wave;
c) spark jet or plasma synthetic jet (PSJ), using microjet.

- physical understanding and numerical modelling of plasma actuators and their interaction with air flows;
- evaluation of the plasma technology for aerodynamic flow control of flow, separation, wing-tip vortex, boundary layer transition, slat noise and aerofoil buffet;
- validation of plasma technology by large wind tunnel tests at realistic Reynolds and Mach numbers;
- demonstration of DBD plasma flow control system using unmanned aerial vehicle (UAV).

More details are given in the complete version of the final publishable summary report, whose outline is provided below:

1.3.1. WP1 - Plasmas devices description and characterisation with and without flow
1.3.1.1. Surface DBD plasma actuators
1.3.1.2. Nanosecond pulsed plasma actuators
1.3.1.3. Spark plasma discharge - The PSJ
1.3.1.4. Summary of the plasmas devices development (WP1)
1.3.2. WP2 - Numerical simulations of plasmas actuators for flow control
1.3.2.1. Modelling of plasma actuators
1.3.2.2. Coupling of computational fluid dynamics (CFD) with advanced plasma models
1.3.2.3. Summary of the plasmas devices modelling and coupling with CFD (WP2)
1.3.3. WP3 - WP4 - Aerodynamic applications
1.3.3.1. Trailing edge limited separation control on a NACA0015
1.3.3.2. Mid-chord separation control on a NACA0015
1.3.3.3. Leading edge full separation control on a NACA0012
1.3.3.4. Trailing edge limited separation control on 3D wing
1.3.3.5. Summary of wind tunnel tests on separation control
1.3.3.6. Wing tip vortex control by plasma actuators
1.3.3.7. Boundary layer transition control with steady and unsteady DBD plasma actuation
1.3.3.8. Attenuation of aerodynamic generated sound from an airfoil equipped with a slat, high lift device
1.3.3.9. High voltage pulsed DBD effects on the airfoil buffet
1.3.3.10. Summary of wind tunnel tests (excepted separations configurations)
1.3.3.11. UAV for plasma flow control
1.3.4. Conclusions and recommendations for future works

Please note that for the sake of clarity and readability, the full description of the main science and technology (S&T) results / foregrounds is included in the complete version of the final publishable summary report, which has been uploaded in SESAM as a PDF file. The full description of the main S&T results / foregrounds is 22-page long and contains about 40 figures.

Potential impact:

Technological impacts

Throughout the years, technology improvements have been made to aircraft and engines to make them more fuel efficient. Efficiency is expected to continue to be improved up to and beyond 2050. One way is aerodynamic improvement for each flight configuration which imposes flow control, both external and internal. With the continued objective of increasing aircraft performances whilst reducing the environmental impact, research is being carried out to find innovative solutions to influence air flow using simple actuators. If the aerodynamic configuration of future aircraft could be modified in real time in flight, then the aircraft's performance could be continually adapted to provide optimum aerodynamic characteristics. Amongst the innovative solutions, the use of plasma technologies has shown itself to be very promising from both a performance point of view and in terms of the diversity in potential applications such as external and internal flow control, combustion enhancement and noise attenuation. The main advantages of plasmas devices are their manufacturing and integration simplicity, low power consumption and ability for real time control at high frequency.

The PLASMAERO project is working to study to improve the flow control using plasmas technology for future generation of air plane in Europe. PLASMAERO is a unique European project where many different actuators have been investigating a variety of related subjects from the plasma physics itself, through to their aerodynamic applications. Flow configuration studies representative of aircraft external flow which can be also exploited for internal flow have been chosen. They are often at the limit of the flight envelope:

- airfoil and ramp separation;
- wing tip vortex;
- boundary layer transition, laminar flow improvement;
- buffet and buffeting;
- slat noise.

The PLASMAERO consortium allows a European benchmarking of the plasma actuators applied to flow control to be performed and will ensure Europe's future sustainable competitiveness and technological leadership in the field of aerodynamics control using plasma actuators. It maximises the dissemination of results within the European Community from both an academic and industrial perspective.

The main technical impact is deeper understanding and the improvement of these systems using plasmas technology and their effect on the principal flow configurations existing on aircraft. The technology readiness level (TRL) level of the DBD and PSJ devices has progressed from TRL2-3 to TRL4. The results have been shared with the scientific community and the European aircraft industry, through several means: the PLASMAERO public workshop, an important number of project publications worldwide, the PLASMAERO public website and through the actions of project partners themselves. Thus, these results can be incorporated into the future studies of these systems and their implementation in the new generations of transport aircraft.

First, PLASMAERO understands, models and classifies, through numerical and experimental studies, the most relevant characteristics of plasma actuators able to influencing flow. For this purpose, various new plasma actuators have been designed and improved for flow control, manufactured and tested (different types of DBDs, fast rise pulsed DBD, FRP-DBD, driven by nanosecond discharges and PSJ). The project has made significant progress on the numerical modelling of plasma actuators and their interaction with flow. This provides a clearer understanding of how plasma actuators can modify a flow. These results, experimental and numerical, are important inputs for the preparation of new control strategy or for validation of strategies developed in PLASMAERO.

Secondly, PLASMAERO demonstrates through wind tunnel experimentations and CFD the ability of plasma devices to significantly improve or control the aerodynamics. These results, experimental and numerical, can be used for preparation of new aerodynamic configurations or for validation of aerodynamic control developed in PLASMAERO.

Thirdly, PLASMAERO demonstrates the integration of these actuators in a reduced size flight platform and their use in real atmospheric conditions. The UAV flight tests in real atmospheric conditions have shown that plasmas devices and their power supplies could be integrated into a reduced size aircraft and that they worked outside of wind tunnels. This result can be used for integration studies in the representative aircraft.

Finally, PLASMAERO provides exhaustive recommendations on future work to achieve the implementation of this technology. These propositions can be following directly or can help industry or the scientific community to perform flow control using plasmas.

These recommendations can be summarised as follows:

a) Plasma actuator developments and understanding of the plasma / flow interaction physics:

It is proposed to pursue the work initiated in the PLASMAERO project in order to:

- Improve or to develop new plasma actuators. These new actuators (steady or unsteady) should allow the validation of the concept of plasma flow control for flow regimes, more representative of those met on aircraft or in engines (Mach value from the high subsonic to supersonic, Reynolds number, etc.).
- Evaluate first, these new actuators in academic test configurations (flat plate, 2D geometry configuration like a single 2D airfoil or a 2D blades cascade) to provide a better understanding of the physical phenomena, and to identify the key parameters for an effective flow control.
- Extend the scope of this evaluation to more severe operating conditions in order to identify their operational limits (resistance of materials and effectiveness of plasma actuators against pressure and temperature).
- Quantify the energy balance of the plasma flow control: aerodynamic gain against the power supplied.
- Compare plasma technology to other flow control technologies (mechanical VG, fluidic VG, MEMS, etc), on the basis of criteria to be determined (aerodynamic parameters, thermodynamic parameters, etc). The plasma is one of the flow control technologies which industrials could use to optimise their applications.

b) Improvement of the simulation models

In order to introduce the plasma technology in the design of industrial applications, it is recommended to continue developments and validation of the simulation models to:

- Provide tools that could provide further understanding of the flow control mechanisms where experimental data is not sufficient to achieve this goal.
- Provide tools that will be differentiating with regards to the choice of the plasma control parameters (number, position and characteristics of the actuators). To achieve an optimal control, such a choice will probably be the result of a combined analysis of the actuators parameters associated to a suitable geometry design.

These developments will have to incorporate more physical modelling:

- Evaluation of the coupled plasma / flow modelling and its comparison with the CFD model technique based on the 'body forces' approach.
- Introduction of the large eddy simulation (LES) type approach and assessment of this model against the Reynolds-averaged Navier-Stokes (RANS) approach.

c) Broadening of the scope of plasma technology applied to other types of flow control

It will be interesting to consider evaluations of this technology to other industrial applications:

- New kind of geometries (duct, blades, etc).
- New types of physical phenomena: acoustics (partly investigated during the project), combustion, aerothermal phenomena, aeroelasticity).

d) PLASMAERO flow configurations assessment

Through CFD and experimental tests representative of industrial applications, high lift and TE separation, B.L. transition, noise.

Socio-economic impact

The PLASMAERO project has permitted the creation of a European concentrated specialist group which demonstrated the advantages of collaborating simultaneously in both the field of plasmas and of aerodynamic with a mixture of different expertise (Plasma science and aerodynamics). During the last steering committee meeting, this group decided to remain in contact and possibly to organise a workshop in the autumn of 2013 where the suite of PLASMAERO would certainly be decided.

It allowed a European benchmarking of the plasma actuators applied to flow control to be performed. It will participate to ensure Europe’s future sustainable competitiveness and technological leadership in the field of aerodynamics control using plasma actuators.

Scientific progress, results and important publications allow the scientific community to be informed and steer ongoing or future research work in this area but also in associated areas such as internal aerodynamics and aerodynamics on land vehicles.

New results can also be included in plasma and aerodynamic university courses.

Presentations, results and the impact of plasmas on aerodynamics shown on the public web site allow the public, and especially the younger generations, to discover this technology and enable creative thinking on the possible environmental impacts on transport vehicles.

The article written in the 'New Scientist' which presents the PLASMAERO project and results in a simplified manner will encourage thought on the application of this technology on futuristic aircraft.

PLASMAERO has brought together the main European actors in this field. The excellent working relationships created during the project, both during its definition phase as well as in its execution has permitted a scientific network, for the time being informal, to be created.

List of websites: http://www.plasmaero.eu
Coordinator's contact details: Daniel Caruana, Office National'Etudes et de Recherches Aérospatiales (ONERA), Tel.: +33-562-252857, E-mail: Daniel.Caruana@onera.fr