Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A new concept to improve power production performance of wind turbines in a wind farm

23.05.2014

Wind energy is one of the most promising renewable energy resources in the world today. Dr. Hui Hu and his group at Iowa State University studied the effects of the relative rotation directions of two tandem wind turbines on the power production performance, the flow characteristics in the turbine wake flows, and the resultant wind loads acting on the turbines.

The experimental study was performed in a large-scale Aerodynamics/Atmospheric Boundary Layer (AABL) Wind Tunnel available at Aerospace Engineering Department of Iowa State University. Their work, entitled "An experimental study on the effects of relative rotation direction on the wake interferences among tandem wind turbines", was published recently in SCIENCE CHINA Physics, Mechanics & Astronomy, 2014, Vol 57(5).


This image shows the ratios of power outputs for the downstream turbine in counter-rotating to those in co-rotating as a function of the spacing between the turbines.

Credit: ©Science China Press

In a typical wind farm, the wind turbine located in the wakes of upstream turbines would experience a significantly different surface wind compared to the ones located upwind due to the wake interferences of the upwind turbines. Depending on the wind turbine array spacing and layout, the power losses of downstream turbines due to the wake interferences were found to be up to 40%.

Therefore, how to improve the power production of downstream wind turbines in a wind farm is one of the most significant research topics in recent years. Extensive experimental and numerical studies have been conducted recently to examine wind turbine aeromechanics and wake interferences among multiple wind turbines in order to gain insight into the underlying physics for higher total power yield and better durability of the wind turbines.

... more about:
»SCP »downstream »experimental

While most of the wind turbines in modern wind farms are Single Rotor Wind Turbine (SRWT) systems, the concept of Counter-Rotating Wind Turbine (CRWT) systems has been suggested in recent years. Since azimuthal velocity would be induced in the wake flow behind a wind turbine with its rotation direction in the opposite direction to the upstream rotor, the downstream rotor should rotate in the same direction as the swirling wake flow for a CRWT system in order to extract wind energy in the wake flow more efficiently.

So far, since the distance between the two rotors in a CRWT system is always very small (i.e., less than 1D, and D is the rotor diameters), the attempts of CRWT to improve wind energy utilization are focused on near wake characteristics. On the other hand, most of the previous studies on the wake interferences among multiple turbines are limited to SRWT systems with all the turbines rotating in the same direction.

The wake interferences among SRWT systems with different rotation directions in a wind farm have never been investigated before. With this in mind, Dr. Hu and his group conducted a comprehensive experimental study to quantify the effects of the relative rotation direction of two tandem wind turbines on the wake interferences among the turbines.

While the oncoming flow was kept constant during the experiments, the model turbines were set to operate in either co-rotating (i.e., the downstream turbine has the same rotation direction as the upstream turbine) or counter-rotating (i.e., the downstream turbine has an opposite rotation direction in relation to the upstream turbine) configuration. The turbine power outputs, the static and dynamic wind loads (i.e., aerodynamic forces and bending moments) acting on the turbines, and the turbulence characteristics in the wake flows behind the turbines were measured and compared quantitatively.

It was found that the turbines in counter-rotating would harvest more wind energy from the same oncoming wind, compared with the co-rotating case. While the recovery of the streamwise velocity deficits in the wake flows was found to be almost identical with the turbines operated in either co-rotating or counter-rotating, the significant azimuthal velocity generated in the wake flow behind the upstream turbine is believed to be the reason why the counter-rotating turbines would have a better power production performance. Since the azimuthal velocity in the wake flow was found to decrease monotonically with the increasing downstream distance, the benefit of the counter-rotating configuration was found to decrease gradually as the spacing between the turbines increases.

While the counter-rotating downstream turbine was found to be able to produce up to 20% more power compared with the co-rotating downstream turbine when the spacing between the turbines was 0.7 rotor diameters (i.e., 0.7D), the advantage of the counter-rotating configuration was found to be reduced to only about 4.0% when the spacing between the turbines was increased to about 5.0D. Since the azimuthal flow velocity in the wake flow was found to become almost negligible in the further downstream region, the benefits of the counter-rotating configuration were found to die away (i.e., <1.0%) when the spacing between the turbines becomes greater than 6.5D.

It suggests that, on the practical relevance of wind farm design, counter-rotating configuration would be more beneficial to onshore wind farms, compared with offshore wind farms, due to the much smaller spacing between the turbines (i.e., ~3 rotor diameters for onshore wind farms vs. 6~10 rotor diameters for offshore wind farms), especially for those turbines sited over the mountains/hills with the spacing between the turbines only about 1~2 rotor diameters.

###

See the article:

Yuan W, Tian W, Ozbay A, Hu H. An experimental study on the effects of relative rotation direction on the wake interferences among tandem wind turbines. Sci China-Phys Mech Astron, 2014, 57(5): 935-949, doi: 10.1007/s11433-014-5429-x

http://link.springer.com/article/10.1007%2Fs11433-014-5429-x

Science China Press Co., Ltd. (SCP) is a scientific journal publishing company of the Chinese Academy of Sciences (CAS). For 60 years, SCP takes its mission to present to the world the best achievements by Chinese scientists on various fields of natural sciences researches.

http://www.scichina.com/

Hu Hui | Eurek Alert!

Further reports about: SCP downstream experimental

More articles from Power and Electrical Engineering:

nachricht Ultra-flat circuits will have unique properties
26.07.2016 | Rice University

nachricht Did you know that UV light helps to ensure safe bathing during the summer months?
25.07.2016 | Heraeus Noblelight GmbH

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: Self-assembling nano inks form conductive and transparent grids during imprint

Transparent electronics devices are present in today’s thin film displays, solar cells, and touchscreens. The future will bring flexible versions of such devices. Their production requires printable materials that are transparent and remain highly conductive even when deformed. Researchers at INM – Leibniz Institute for New Materials have combined a new self-assembling nano ink with an imprint process to create flexible conductive grids with a resolution below one micrometer.

To print the grids, an ink of gold nanowires is applied to a substrate. A structured stamp is pressed on the substrate and forces the ink into a pattern. “The...

Im Focus: The Glowing Brain

A new Fraunhofer MEVIS method conveys medical interrelationships quickly and intuitively with innovative visualization technology

On the monitor, a brain spins slowly and can be examined from every angle. Suddenly, some sections start glowing, first on the side and then the entire back of...

Im Focus: Newly discovered material property may lead to high temp superconductivity

Researchers at the U.S. Department of Energy's (DOE) Ames Laboratory have discovered an unusual property of purple bronze that may point to new ways to achieve high temperature superconductivity.

While studying purple bronze, a molybdenum oxide, researchers discovered an unconventional charge density wave on its surface.

Im Focus: Mapping electromagnetic waveforms

Munich Physicists have developed a novel electron microscope that can visualize electromagnetic fields oscillating at frequencies of billions of cycles per second.

Temporally varying electromagnetic fields are the driving force behind the whole of electronics. Their polarities can change at mind-bogglingly fast rates, and...

Im Focus: Continental tug-of-war - until the rope snaps

Breakup of continents with two speed: Continents initially stretch very slowly along the future splitting zone, but then move apart very quickly before the onset of rupture. The final speed can be up to 20 times faster than in the first, slow extension phase.phases

Present-day continents were shaped hundreds of millions of years ago as the supercontinent Pangaea broke apart. Derived from Pangaea’s main fragments Gondwana...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

GROWING IN CITIES - Interdisciplinary Perspectives on Urban Gardening

15.07.2016 | Event News

SIGGRAPH2016 Computer Graphics Interactive Techniques, 24-28 July, Anaheim, California

15.07.2016 | Event News

Partner countries of FAIR accelerator meet in Darmstadt and approve developments

11.07.2016 | Event News

 
Latest News

New study reveals where MH370 debris more likely to be found

27.07.2016 | Earth Sciences

Dirty to drinkable

27.07.2016 | Materials Sciences

Exploring one of the largest salt flats in the world

27.07.2016 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>