Numerical verification of a new load alleviation technique for wind turbines in atmospheric turbulence

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The common purpose of the research focus is the improvement of calculation methods for wind turbines in turbulent atmospheric inflow, the investigation of the occurring complex interactions and load cycles, the experimental and numerical study of a novel load alleviation concept and its influence of the aerodynamics of the turbine, the loads and the wake.The first main objective in the proposed prolongation phase (36 months) for the present sub-project is the extension of the numerical setup and process chain for CFD simulations of wind turbines with kinematically coupled leading and trailing edge flaps under turbulent inflow conditions. This will be done by implementing a fluid-structure coupling to determine the transient flap deflection, considering all acting forces, instead of prescribing them, as it was done up to now. The CFD code (FLOWer) will determine the unsteady aerodynamic forces and moments on the flaps and pass them to the CSD code (SIMPACK). There, the inertias and the weight forces will be calculated and the flap deflection will be determined. This will be done in a time-accurate manner for every physical time-step considered in the unsteady CFD simulation. To evaluate the load control concept under investigation and to study the occurring aerodynamic effects, the complexity of the system will be increased successively (starting from a 2D airfoil with leading edge and trailing edge flaps at steady inflow up to a full size wind turbine under turbulent atmospheric inflow conditions). The unsteady flap deflections will be calculated directly in all simulations. The extended process chain is verified by comparison with experimental data from two wind tunnel campaigns of profiles with load control concept and with wind tunnel data of a model rotor with load control. The validated code is then used to simulate the generic NREL 5MW wind turbine.The second main objective is the investigation of the influence of flaps for a turbine at non rated conditions. These operating conditions cause deterministic load fluctuations combined with unsteady aerodynamic effects, which were not investigated in the first two project phases but have a significant impact on the life time of a wind turbine. Therefore, they are an important element in the evaluation of the effectiveness of the load control. The studies of these cases lead to an extension of the scope of investigated load cases and to a more realistic view on the overall loads over the life time of a wind turbine.The new objectives can only be achieved thanks to investigations and code extensions done in the first two project phases. Moreover, the simulations performed during this time can now be used for comparative purposes. For the validation of the new extensions, wind tunnel measurement are necessary again and therefore, the close link between experiment and simulation will continue to exist.