Within tests during the INNWIND.EU project, a model offshore wind turbine has been placed in the jet of a wind generator whose outlet size is similar to the rotor area. This paper deals with the CFD (Computational Fluid Dynamics) simulation of this turbine in a simplified experimental environment. As this is a preliminary study to evaluate the influence of the jet flow, no comparison to experimental results is done. The loads on the wind turbine are evaluated and compared to a uniform inflow case. The study is focused on the thrust which is the biggest acting force and most important for floating turbine motion. The results show that the thrust of the whole rotor is comparable to the unifonn inflow case although there are bigger differences in the spanwise distribution for a single blade. Hence, it can be concluded that the model turbine in the jet flow is suitable for the experiments as long as it is guaranteed that the turbine is placed in the center of the jet at the investigated distance to the wind generator.
The INNWIND. EU Project is dealing with investigations on large offshore wind turbines of the 1O:MW class. Basis of the investigations is the three bladed horizontal axis 10 MW DIU reference turbine (Bak, Zahle, Bitsche, Kim, Yde, Henriksen, Andersen; Natarajan, Hansen). To install this large turbine at offshore sites, new platform concepts are investigated for bottom fixed as well as for floating installation. Different codes are used to simulate the turbine on the platform. To simulate the floating platform, codes for aerodynamics, hydrodynamics as well as structural analysis are combined. The only way to validate the numerical results experimentally within the project is wave tank testing using a scaled model of the platform. These tests have been performed at Ecole Centrale de Nantes, France (ECN). On the one hand platform only tests have been conducted to evaluate the suitability of the hydrodynamic simulations using a Froude scaled model of the platform. On the other hand tests of the entire system, including turbine and platform have been performed. The geometric scaling factor is 1/60 and the scaling factor for the velocity is 1/601/2. Therefore a model turbine has been developed by Politecnico di Milano, Italy (POLIMI). It operates at the same tip speed ration (TSR) as the DTU reference turbine and has been designed for similarity of the thrust coefficient using a low Reynolds number airfoil (RG 14) for all sections excluding the cylindrical root. As it is operating at very low Reynolds numbers (~45000 in the present case), it is not possible to match the power coefficient of the full size turbine which is much higher than for the model turbine. As the motion of the turbine is mostly influenced by forces, the mismatch in power and respectively torque is expected to be negligible and the thrust is representative. This is a common approach, also presented in other publications like Make, Vaz, Fernandes, Bunnester and Gueydon (2015), which deals with the need of blade redesign for scaled model offshore wind turbines using CFD and BEM (Blade Element Momentum). Gueydon, Venet and Fernandes (2015) are presenting an optimization process for the simulation of the aerodynamics of a floating offshore wind turbine with a BEM approach. To match the measured Cp and CT they adjusted the polars with different approaches. Additionally, they show that the thrust coefficient in the referenced measurements could be match best using 3D CFD simulations.
