High Fidelity Simulation of Multi-MW Rotor Aerodynamics by Using a Multifan

During the last decades the offshore wind energy sector has experienced large developments. Despite bottom fixed wind turbines have been widely used, some their limitations have brought to scout and develop concepts based on floating support structures. The behavior of such structures is affected by forces of different nature, so the analysis of these structural systems becomes complex and requires an accurate definition of their dynamics. This is one of the reasons for which the numerical simulations can be highly improved from experimental tests at reduced scale. The interaction between hydrodynamic forces and the structure is investigated experimentally by means of wave tank tests. In these circumstances the correct representation of the aerodynamic forces is not trivial due to laboratory scale law conflicts. These issues can be eased by using hybrid systems. This work aims to describe a hybrid system developed by IH Cantabria. The system is meant to define the most significant aerodynamic loads affecting the dynamic performance of a floating wind turbine by using an aerodynamic model (BEM), while their generation in the scaled model is obtained by using a multi-fan system. This approach successfully satisfies issues related to the scalability of the aerodynamic forces and their variability due to the turbine controller and wind variability. Nevertheless, some shrewdness have to be taken in order to comply with the following matters. The correct representation of the dynamic effects relative to the aerodynamic forces requires high frequency calculations. For this reason some simplifications on the aerodynamic model must be taken. This work explains the criteria used to define the simplifications to be adopted, showing the low impact they have on the tests results. On the present paper it will be demonstrated the capabilities of the multi-fan that was chosen to reproduce the rotor aerodynamics. Moreover, it will evidence the high fidelity of the forces developed by the multi-fan, both in terms of amplitude and reactiveness on the forces fluctuations. The final section will prove the ability of the hybrid system to reproduce with high fidelity and large flexibility the aerodynamic load conditions desired in lab scale wave tank tests.