Scaling Methodology for Floating Wind Turbines
Author Sébastien Gueydon (MARIN), Gerson Fernandes (MARIN Academy)
Title Scaling Methodology for Floating Wind Turbines
Conference/Journal EWEA
Year 2013

Summary
When the water depth and soil conditions make it difficult to install fixed foundations for wind turbines, floating foundations may be preferred. Of course a floating foundation brings new challenges to the turbine. Those challenges can be addressed by accurate numerical simulations that include the effects of the motions of the floater on the turbine’s loads and vice-versa. Several codes have been recently developed for that purpose. To improve their accuracy, these codes need to be calibrated. This can be done in wave basins at reduced scale. Ideally a physical model of the floater on which a turbine is mounted is used. Only then the interaction between the hydrodynamic response of the floater and the aerodynamic loads can realistically be investigated.
The model tests of a floating structure in a wave tank aims at accurately assessing the motions of the floater. For the kind of floating foundations envisaged here, the best practise is to scale down the floater according to Froude scaling laws. Unfortunately, this scaling does not work for the rotor. It has been observed that the aerodynamic loads of the scaled down rotor are much smaller than the equivalent loads at full scale. It was necessary to study the air flow around the rotor to understand what’s happening with the scaled down rotor. In the basin, the flow separates closer to the leading edge of the blade than in real conditions. Consequently the rotor’s thrust and torque drop and the turbine performs badly. Another scaling approach is required for the rotor to scale its performance rather than its geometry. In the novel approach applied at MARIN, the blades are re-designed for the flow regime experienced at model scale. In this way the rotor’s performance

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