Analyzing scaling effects on offshore wind turbines using CFD

In this paper the flow over two (floating) wind turbines has been studied using RANS CFD calculations at model and full-scale Reynolds numbers conditions. The well-known NREL 5 MW and MARIN designed turbines (MARIN Stock Wind Turbine or MSWT) have been analysed. The MSWT was designed to have the same thrust at model-scale as the NREL turbine at full-scale conditions. The thrust was the major driver since it is more important for the behaviour of the floating platform. Numerical sensitivity studies were done to minimize all possible uncertainties: domain size, iterative convergence, grid refinement, and turbulence model sensitivity was studied. Modern verification and validation procedures were used to assess those uncertainties and to perform a validation of the numerical results against experimental data coming from constant uniform inflow, fixed turbine experiments. Furthermore, the flow around the turbines and its performance, both for model and full-scale, have been scrutinised, compared, and insights into their behaviour and Reynolds/scale effects gained. A good agreement between the CFD results and the experimental data has been obtained, with low uncertainties for thrust but large uncertainties for power. The large Reynolds effects on the flow of these turbines have been also shown and explained. Finally, it has been confirmed that the MSWT performs as intended at model-scale conditions.