7. CONCLUSIONS
In this work the variable tip sweep capability control concept is incorporated in the 5MW NREL reference wind turbine on a purely aerodynamic model. The originality that this research work incorporates is that the investigation is performed with a simple – engineering BEM model modified for tip swept rotors which is based on a more analytical model based on ULL theory. The early results from the parametric study with the ULL model that also agree with the results of the BEM model, indicate that there is a good potential in using active blade tip sweeping concept as a constant fatigue load alleviator or a safety feature during wind gusts. The improvement is noticeable in the 5MW reference wind turbine and could be more significant for larger wind turbines that experience higher tip speeds and deflections. However, power increase can only be achieved passively utilizing blade span extension combined with tip sweeping. In every case, there will be a trade off of benefits and drawbacks. For the fixed solution which is investigated first there will be an AEP increase with similar loads but this will add cost to the production phase 696 expressed as extra development and constructions costs. Regarding the active solution, there will also be a gain in AEP accompanied with reduced fatigue / extreme loads but in this case the extra costs will be even more. As part of a future work there is a need to select the type of the actuator that will move the tip and design a suitable stable controller based on aeroelastic predictions, too. Of course this actuator will add weight to the structure and in addition would require the establishment of a maintenance plan which in turn 71 raises the functional costs. The proposed solution is based on a simple controller and its performance could be improved with the design of an advanced controller that could provide more load regulation. The target of the proposed concept is to evaluate the benefits of an innovative conceptual active sweep controller and not to provide the optimal solution.
