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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
Tetsuya Wakui Osaka Prefecture University, Japan
Co-authors:
Tetsuya Wakui (1) F Masanori Yonesugi (1) Ryohei Yokoyama (1)
(1) Osaka Prefecture University, Osaka, Japan

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Presenter's biography

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

Dr. Wakui has been studying on wind power generation from the viewpoint of the system engineering approach. He is currently an associate professor at the department of mechanical engineering, Osaka Prefecture University. After getting the Ph.D. in the optimal design and control of stand-alone wind turbine generator systems in 2001, he spent 4 years at Waseda University and then transferred to the current university. The current his study focuses on the optimal control for floating offshore systems as well as grid-connected and stand-alone systems and the optimization of distributed energy supply systems.


Poster

Poster Download poster (6.87 MB)

Abstract

Performance Analytical Model of Vertical Axis Wind Turbines for Floating Offshore Applications

Introduction

Floating offshore wind turbine-generator systems are expected to install in areas that have very deep waters. Currently, several demonstrating projects to commercialize floating offshore systems are being carried out in Europe, United States, and Japan. In these projects, conventional horizontal axis wind turbines are employed. However, vertical axis wind turbines possess great potential for floating offshore systems. This is because they excel in stability of a floating platform due to a generator and gearbox installed near an oscillation center. There is a paucity of demonstrating projects using vertical axis wind turbines in comparison with horizontal axis wind turbines.

Approach

To conduct a feasibility study on floating offshore systems using vertical axis wind turbines, an performance analysis of these wind turbines under an inclined axis condition caused by a platform motion is indispensable. Thus, the present study develops a performance analytical model of vertical axis wind turbines for floating offshore systems by extending a conventional multiple streamtube model to inclined axis conditions. Then, the impact of the inclined axis angle on the performances of a straight-wing vertical axis wind turbine is analyzed.

Main body of abstract

In the developed model, it is assumed that only the perpendicular component of the inflow wind to the blade element contributes to generating torque. On this assumption, the inflow wind after passing through the upstream blade is blown up because the wind speed of the horizontal component to the blade element is maintained. Thus, each streamtube, which corresponds to each control volume, has two break points at the upstream and downstream blade elements. Further, the downstream blade is uniquely classified into two zone. In the first zone, the wind attenuated at the upstream blade element inflows to the downstream blade element in the same streamtube. In the second zone, the wind that is not attenuated due to the inclined axis inflows to the downstream blade element. To determine these two zones in the downstream blade, the average blow-up angle of the winds after passing through the upstream blade elements and the generating torque of the upstream blade during half rotation are first calculated using the multiple streamtube theory. Then, the generating torque of the downstream blade during half rotation is calculated using the wind speeds in the streamtubes corresponding to the classified zones and the blow-up angle.
The analyzed wind turbine is a three-blade straight-wing vertical axis type. The rotor diameter, rotor height, and blade chord length are 100, 100, and 5 m, respectively. The blade airfoil is NACA0015. The calculated result shows that the maximum power coefficient in the inclined axis angle of 5 deg to the leeward side is increased by 3.3% from the result under no inclined axis condition. This is because the negative generating torque of the downstream blade is reduced by the wind not attenuated at the upstream blade element. Moreover, the impact of the inclined axis angle on the wind turbine performances derived by the developed model is similar to the experimental result by Mertens et al. (Journal of Solar Energy Engineering, Vol. 125, 2003).


Conclusion

The performance analytical model of vertical axis wind turbines for floating offshore systems, developed in the present study, is characterized by considering the blow-up behavior of the wind after passing through the upstream blade element and the inflow wind speed distribution in the downstream blade due to the blow-up wind. The calculation result reveals the mechanism of the slight increase in the maximum power coefficient under inclined axis conditions.


Learning objectives
The present study provides the new insights regarding the aerodynamic behavior of a vertical axis wind turbine under inclined axis conditions, especially the blow-up behavior after passing through the upstream blade. The developed model can be applied to the performance analysis of floating offshore systems using vertical axis wind turbines.