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Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 and 16:00-17:00 on Thursday, 19 November 2015.

Lead Session Chair:
Stephan Barth, ForWind - Center for Wind Energy Research, Germany
Yusuke Otake Hitachi, Ltd., Japan
Co-authors:
Yusuke Otake (1) F P Soichiro Kiyoki (1) Shigeo Yoshida (2)
(1) Hitachi, Ltd., Hitachi-shi Ibaraki-ken, Japan (2) Kyushu University, Kasuga-shi Fukuoka-ken, Japan

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Yusuke Otake has been working in Hitachi for a year, and he has been assigned to research about wake in wind farm. Before he started working in Hitachi, he studied computational fluid dynamics. He received his ME in Computational Science and Engineering at Nagoya University in 2014.


Poster

Poster Download poster (11.69 MB)

Abstract

Effects of turbulence intensity distributions in wake on fatigue-damage

Introduction

The objective of this study was to investigate the effect of turbulence intensity distribution on fatigue-damage in a wind farm (WF).
Wind turbine damage is generally calculated using a wake flow (wake) as an inflow condition. A wake often occurs behind the wind turbine due to the wind passing through the turbine. Furthermore, a wake is known to decrease wind speed and increase turbulence intensity. Therefore, for a wind turbine located at a WF, the wind power output decreases and wind turbine damage increases due to the wake.

Approach

If we use a conventional wake calculation model recommended by the International Electrotechnical Commission (IEC), calculated fatigue-damage in some cases is bigger than those found from the measurement. We presume that the reason for this discrepancy may be due to the fact that the IEC recommended model ignores the decrease in wind speed and turbulence intensity is assumed to be uniform.
We focused on the turbulence intensity distribution in a wake to improve the precision of fatigue damage calculation. Actual turbulence intensity distribution tends to become bell shaped based on various experimental studies. Therefore, we assumed that the turbulence intensity distribution can be approximated with a Gaussian distribution as a general bell shaped distribution. Therefore, we proposed a new model by using a Gaussian distribution.

Main body of abstract

We evaluated the difference in the IEC and proposed models based on suitability for measurement result. For this study, we used damage equivalent load (DEL) as the parameter for calculating fatigue damage.
For this evaluation, we assumed two wind turbines placed in line and calculated actual DEL by measuring the strain measurement value at the tower base and blade root. To obtain DEL at an actual WF, we conducted aero elastic analyses by using the two models.
We compared the measured and calculated values to evaluate the effect of a wake by using the DEL ratio, which is calculated as the ratio of DEL in wake to DEL out of wake.

Conclusion

From the results, we confirmed that the analysis value was about 21% larger than measured value with the proposed model, whereas the analysis value was about 31% larger than the measured value with the IEC model at the tower base. We also confirmed that the analysis value was about 5% larger than the measured value with the proposed model, whereas the analysis value was about 12% larger than the measured value with the IEC model at the blade root.
Compared to the IEC model results, the proposed model has the potential to precisely estimate the experimental value. By considering the turbulence intensity distribution, we can adequately evaluate wind turbine damage at a WF.


Learning objectives
Not only turbulence intensity increases, but wind speed decreases due to the wake. For future work, it will be necessary to consider turbulence intensity distribution and wind velocity distribution together to more accurately predict DEL.
A wake model is used some technologies to determine the most suitable placement of wind turbines and improve operational efficiency of a WF. Therefore, we have to continue discuss the adequateness of wake models.