19 Aug 2021

19 Aug 2021

Review status: this preprint is currently under review for the journal WES.

Vertical wake deflection for floating wind turbines by differential ballast control

Emmanouil M. Nanos1, Carlo L. Bottasso1, Dimitris I. Manolas2, and Vasilis A. Riziotis2 Emmanouil M. Nanos et al.
  • 1Wind Energy Institute, Technische Universität München, 85748 Garching b. München, Germany
  • 2School of Mechanical Engineering, National Technical University of Athens, 15780 Athens, Greece

Abstract. This paper presents a feasibility analysis of vertical wake steering for floating turbines by differential ballast control. This new concept is based on the idea of pitching the floater with respect to the water surface, thereby achieving a desired tilt of the turbine rotor disk. The pitch attitude is controlled by moving water ballast among the columns of the floater.

This study considers the application of differential ballast control to a conceptual 10 MW wind turbine installed on two platforms, differing in size, weight and geometry. The analysis considers: a) the aerodynamic effects caused by rotor tilt on the power capture of the wake-steering turbine and at various downstream distances in its wake; b) the effects of tilting on fatigue and ultimate loads, limitedly to one of the two turbine-platform layouts; and c) for both configurations, the necessary amount of water movement, the time to achieve a desired attitude and the associated energy expenditure.

Results indicate that – in accordance with previous research – steering the wake towards the sea surface leads to larger power gains than steering it towards the sky. Limitedly to the structural analysis conducted on one of the turbine-platform configurations, it appears that these gains can be obtained with only minor effects on loads, assuming a cautious application of vertical steering only in benign ambient conditions. Additionally, it is found that rotor tilt can be achieved in the order of minutes for the lighter of the two configurations, with reasonable water ballast movements.

Although the analysis is preliminary and limited to the specific cases considered here, results seem to suggest that the concept is not unrealistic, and should be further investigated as a possible means to achieve variable tilt control for vertical wake steering in floating turbines.

Emmanouil M. Nanos et al.

Status: open (until 04 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of WES paper.', Anonymous Referee #1, 14 Sep 2021 reply
  • RC2: 'Comment on wes-2021-79', Anonymous Referee #2, 20 Sep 2021 reply

Emmanouil M. Nanos et al.

Emmanouil M. Nanos et al.


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Short summary
A novel way of wind farm control is presented, where the wake is deflected vertically to reduce interactions with downstream turbines. This is achieved by moving ballast in a floating offshore platform, in order to pitch the support structure and thereby tilt the wind turbine rotor disk. The study considers the effects of this new form of wake control on the aeorodynamics of the steering and wake-affected turbines, on the structure, and on the ballast motion system.