Numerical Simulation On Tower Shadow Effect Of HAWTs

The change of aerodynamic performance, which is caused by the interaction of blades and tower in HAWTs, is called Tower Shadow Effect. Tower shadow effect has great influence on performance of HAWTs. Therefore, it is necessary to estimate Tower Shadow Effect. However, many constraints exist in experiment method on Tower Shadow Effect, CFD method is applied in this paper.First of all, a full 3D Wind Turbine Numerical Model is established on the basis of NREL Ames low speed wind tunnel tests, then steady computation is carried out with the purpose of proving the validity and reliability of this model. Based on the steady results, unsteady computation is carried out later. The unsteady results do not show good agreement with experimental measurements as the constraints of computation conditions.As many constrains exist in the full 3D Wind Turbine Numerical Model, a Wind Turbine Blade Clip Model, which is based on the Blade Element - Momentum Theory, is proposed. It assumes that the chosen blade clip can be seen as a blade element, which means the adjacent blade clips have no interaction between each other, or span flow is ignored. Then, similarly, steady computation is carried out to prove the correctness and reliability of this model. Unsteady computation is carried out later based on the steady results. The unsteady results show good agreement with the experiment measurements, and the tower shadow effect is good reflectedThe reliability of the Wind Turbine Blade Clip Model has been proved. Now, change the distance between blade rotation plane and tower, then study the relationship between the distance and the Tower Shadow Effect. Comparison of different distance shows that the closer the distance is, the stronger the interaction between blades and tower is, and the more obvious the Tower Shadow Effect is. Oppositely, the further the distance is, the weaker the interaction between blades and tower is, and the less obvious the Tower Shadow Effect is. The interaction can be ignored when the distance is big enough.The Wind Turbine Blade Clip Model is based on blade element assumption, which means span flow is ignored, therefore, this model is not suitable in the situation which has great span flow cause by high wind speed and high rotation speed, it is recommended that correction formula should be introduced. On the other hand, the Wind Turbine Blade Clip Model is just a simplified model, it can't accurately show the true 3D flow. Therefore, optimization of the full 3D Wind Turbine Numerical Model is suggested to achieve a good agreement with true fluid flow.