Realistic simulation of aerodynamic loading for model testing of floating wind turbines

Day, Alexander H and Clelland, David and Oguz, Elif and Dai, Saishuai and Azcona Armendáriz, José and Bouchotrouch, Faisal and Lopez, Juan Amate and Sánchez, Gustavo and González Almeria, Gonzalo; (2017) Realistic simulation of aerodynamic loading for model testing of floating wind turbines. In: The 5th International Conference on Advanced Model Measurement Technology for the Maritime Industry (AMT'17). University of Strathclyde, GBR, pp. 419-432.

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Abstract

The simulation of wind loading for tank testing of floating wind turbines presents a variety of severe challenges. The floating platform naturally responds to wave loadings which are Froude-scaled, whilst the turbine forces respond to aerodynamic loads which are Reynolds-scaled. It is possible to account for Reynolds effects by appropriate distortion of the rotor geometry, nonetheless, construction and operation of a working scale rotor is extremely challenging due to the large size, very light weight, and complex control requirements, while relatively few wave tanks have the ability to generate suitable wind fields. The current study reviews the approaches used to simulate wind loading on floating wind turbines in wave tanks and describes the deployment of an "software in the loop" (SIL) approach in which the thrust component of the wind load is generated using a high-speed fan located on the model in line with the rotor drivetrain. The six-degree-of-freedom platform motion is measured during the tests, and the aerodynamic thrust related to the instantaneous position and velocity of the platform is calculated in real time using a modified version of the well-known FAST aero-hydro-servo-elastic software code. This calculated thrust is then used to control the fan speed to generate the physical thrust in the model test. Using this approach it is possible to explore the impact of different wind environment, rotor configurations, and control strategies without the need for a complex model of the rotor, and without generation of wind over the tank. In the present study, the approach is deployed for an innovative shallow water tension-leg platform (TLP) developed by Iberdrola. The impact of the SIL approach is compared for a variety of wind directions with results generated in two baseline conditions: the conventional case with no wind loading and a simplified case with a constant wind loading. Results are shown for the impact of the wind loading on the platform motions for free oscillation tests, and regular wave RAOs. The challenges of the approach along with the advantages and disadvantages in comparison to other methods for wind load simulation on floating wind turbines are discussed, and the scope for further improvements in the realism of wind load simulation in physical model tests of floating wind turbines is explored.

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