Fluid-structure coupled investigations of the NREL 5 MW wind turbine for two downwind configurations

This work investigates the performance of a wind turbine in a downwind configuration using two different tower concepts. Being subjected to the tower shadow, wind turbine blades on downwind machines can experience higher loads compared to upwind turbines. Using alternative tower types like truss towers could influence those negative effects and therefore affect the performance of the downwind machines. For this purpose, an in-house framework for fluid-structure coupled CFD computations is used and numerical simulations are conducted on the NREL 5 MW wind turbine for two different tower concepts, namely a tubular and a truss-type tower geometry. To quantify the effect of the tower shadows on the rotor performance, first the isolated tower geometries are investigated. In the second step, the complete wind turbine with flexible blades is simulated. The obtained numerical results indicate, that the truss tower causes a more severe tower shadow than its tubular counterpart, which also recovers slower. Following that, the wind turbine blades experience more pronounced reductions in global and local forces for the truss tower configuration. Furthermore, both downwind turbine types show significant torsional blade vibrations caused by the crossing of the tower shadow. In terms of blade deflections, only small deviations can be observed.