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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Wakes: Do we need different models for onshore and offshore wind farms?' taking place on Wednesday, 12 March 2014 at 16:30 -18:00. The meet-the-authors will take place in the poster area.

Atsutoshi Muto The Japan Steel Works Ltd., Japan
Co-authors:
Atsutoshi Muto (1) F P Jun Suzuki (1) Hiroyuki Suzuki (1) Yasuhiro Fujita (1)
(1) The Japan Steel Works Ltd., Muroran, Japan

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Mr. Muto is a manager of research laboratory of The Japan Steel Works ltd., wind turbine manufacturer in Japan. He is responsible for an evaluation of loads working on a wind turbine, power performance, a site assessment for windfarm installed on complex terrain and so on. His researches are based on fluid dynamics and structural mechanics.

Abstract

Wind turbine wake analysis including wind direction fluctuation correction

Introduction

In recent years, in Japan, coastal areas where the wind conditions are suitable for wind turbine construction have become saturated with already constructed wind turbines. Therefore, new wind turbines are increasing being installed in inland areas, and, in particular, tend to concentrate on the mountains areas in where high wind speeds can be expected. Additionally, wind turbines tend to be installed at high densities. In such windfarm sites, high levels of turbulence are generated by the terrain and by the wake of neighboring wind turbines. Therefore, a precise prediction of turbulent intensity becomes more and more important.

Approach

Today, the equation shown in 61400-1 IEC Ed.3 Annex D is the only method to evaluate wind turbine wake. However, it was established for wake of wind turbines installed in flat terrain or offshore and cannot apply to them installed in complex terrain. Then, in this study, in order to analyze wind turbine wake in complex terrain, CFD analyses in a flat terrain with an actuator disk model as wind turbines are carried out as the previous step to an analysis in a complex terrain. In addition, analysis results are compared with measured wind turbine wake by a meteorological mast.

Main body of abstract

An influence range by wind turbine wake was identified by the results of CFD analysis. The wind velocity deficit area was distributed behind the wind turbine over a range of about 10D (D: rotor diameter) in the wind direction and 1.5D in the transverse direction. In addition, the area of the turbulence intensity increased by wake was distributed over a range of about 10D in wind direction and about 3D in transverse direction. These results coincide to a minimum distance of the wind turbine installing known in general. Compared with the results measured at the met mast, analysis results tend to be narrower distributions and to show higher values in both wind velocity deficit region and increased turbulence intensity region due to a wake. This is because wake propagation is affected by a wind direction change in actual wind turbine while a wind direction of inflow wind in analysis is constant. Therefore, in this study, a correction to analysis results by using the observed value of wind direction changes is carried out. The corrected results are obtained by adding analysis results obtained from analysis result for different wind directions having an occurrence probability calculated from standard deviation of an observed wind direction change.

Conclusion

In the corrected analysis result, a value, a region of both wind velocity deficit and turbulence intensity increased due to a wake coincided with observation value with an actual wind turbine well, and improvement of prediction precision was confirmed. An application is possible to a complex terrain since this technique can consider wake in conventional CFD. After this, comparison with measured wake generated by a wind turbine installed on a complex terrain will be tried, and precision of analysis will be tried to be improved.


Learning objectives
Since wind direction fluctuation is different by a site and climatic conditions, then propagation of wind turbine wake is also different. Therefore, it is important to take site specific wind direction fluctuation into consideration for analyzing wind turbine wake.