Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Successful wind tunnel test of controllable rubber trailing edge flap for wind turbine blades

23.02.2010
For some years, the Wind Energy Division at Risø DTU has been working to develop a method for controlling the loads on large wind turbine blades using a flexible trailing edge made of an elastic material which can be controlled by means of compressed air or hydraulics. Now, the invention, which has been called CRTEF (Controllable Rubber Trailing Edge Flap), has been tested in a wind tunnel with promising results.

Today’s wind turbine blades, which can measure more than 60 metres in length, are subjected to enormous loads, which means that a blade can flex as much as 4-6 metres during strong gusts. However, the blades are also so long that there can be considerable differences in the loading from the gusts along the blade. In wind farms, surrounding wind turbines also exert considerable influence and generate turbulence, which has a more localised effect.

“It is these local influences which we hope our design will help mitigate. However, in addition to our rubber trailing edge, it also calls for effective sensors and control systems which can tell the system to regulate the flaps according to the local wind conditions along the blade. Right now we are looking at different types of sensors and a trailing edge made of plastic instead of rubber,” explains Research Specialist Helge Aagaard Madsen.

In December 2009, the rubber trailing edge was tested in the open jet wind tunnel at the company Velux in Denmark. The test marked the end of a development process which was initiated in 2006. It started with a GAP funding project which ran from 2007 to 2008 and confirmed the operating principle. This was followed by the current project in 2009, supported by Region Zealand, where the rubber trailing edge was tested in the wind tunnel. Along the way, many different prototypes have been developed and manufactured at the Fibre Laboratory at the Materials Research Division at Risø DTU, which also has been part of this development process.

“The operational principle which we have arrived at is very simple and robust, and we also believe that the manufacturing process will be so. The wind tunnel test showed, among other things, that the outward curve of the flap does not change markedly when subjected to wind loads similar to those on a real turbine blade. In addition, we measured the correlation between the deflection of the flap and the change in lift on the blade section. This produced figures which we can enter into our calculation models and then realistically simulate how the flap will reduce the loads on the turbine,” says Helge Aagaard Madsen.

“A further bonus of our design is that the moulded rubber trailing edge gives us a sharp edge which produces less noise and greater output. As most blades today are manufactured in two halves and afterwards joined together, the trailing edge will always have a certain thickness. The trailing edge is then ground to make it thinner, but with our design, the blade automatically gets a completely sharp edge.”

Up to a moderate gale
The test facilities at Velux have been used in the past to test wind turbine blade profiles, so it was obvious that the design should be tested here. In the wind tunnel it is possible, among other things, to regulate the wind speed, and the blade profile can be turned to simulate a change in wind direction in relation to the profile.

The test set-up consisted of a two-metre-long blade section with a total chord of one metre and a 15 cm rubber flap covering the entire span. The blade incorporated a pneumatic system for controlling the flexible silicone material which the trailing edge is made of. Finally, two sensors were attached to the front of the blade which measured wind direction and speed.

“So far there has been focus on demonstrating and testing the operating principle, but now where we can see that it is a robust and reliable model, which can withstand the strong wind loading, we can start to focus more on optimising the design and working towards a full-scale version,” says Helge Aagaard Madsen, adding that one of their concerns was whether strong gusts of wind would counteract the deflection of the rubber trailing edge, which the compressed air caused. But fortunately it was not the case.

The force which the blade is exposed to is based on measurements of the surface pressure across the blade section. The difference in the force on the upper side and lower side of the blade clearly indicates how the movements of the rubber trailing edge can regulate this force and thereby compensate for the fluctuating forces to which a blade is otherwise subjected because of wind gusts.

“Among other things, we investigated how quickly the rubber trailing edge could regulate, and we tested the flaps to a frequency above 2 Hz. Today, pitch is regulated by turning the entire blade around a bearing at the hub, but this has limitations due to the blade weight of several tons but also because a distributed, variable regulation along the blade is not possible. Consequently, we believe that the control with flaps can supplement the slower pitch regulation really well,” explains Peter Bjørn Andersen.

A step on the way to full-scale
Now that the operating principle has been thoroughly tested, the next step in the project is to develop the technology towards a stage where the rubber trailing edge flap is ready for testing in a full-scale prototype model. The researchers will work on optimising the design so the deflection will be as big as possible for a given pressure in the voids within the trailing edge. Durability is another important issue, as is developing systems for supplying compressed air or hydraulic power.

“We are in contact with a number of companies who are interested in working with us on these issues, and it is vital for the further development of the technology that we involve industry as this is where the systems will be manufactured at the end of the day. The plan is thus to launch a new development project which involves close corporation between on one side the research groups at Risoe DTU in the Wind Energy Division and in the Materials Research Division and on the other side these companies in order to bring the rubber trailing edge flap technology to a stage where it is ready for testing on a full-scale wind turbine,” concludes Helge Aagaard Madsen.

Helge Aagaard Madsen | EurekAlert!
Further information:
http://www.risoe.dtu.dk
http://www.risoe.dtu.dk/News_archives/News/2010/0210_gummibagkant.aspx?sc_lang=en

More articles from Power and Electrical Engineering:

nachricht Failures in power grids: Dynamically induced cascades
25.05.2018 | Technische Universität Dresden

nachricht Beyond the limits of conventional electronics: stable organic molecular nanowires
24.05.2018 | Tokyo Institute of Technology

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Powerful IT security for the car of the future – research alliance develops new approaches

The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.

Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...

Im Focus: Molecular switch will facilitate the development of pioneering electro-optical devices

A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.

The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...

Im Focus: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

In focus: Climate adapted plants

25.05.2018 | Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

 
Latest News

In focus: Climate adapted plants

25.05.2018 | Event News

Flow probes from the 3D printer

25.05.2018 | Machine Engineering

Less is more? Gene switch for healthy aging found

25.05.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>