Development of an actuator disk model for large eddy simulations of the Helix wind farm control approach

Abstract

The Helix approach is a dynamic control method that mitigates wind turbine wake effects by pitching the turbine blades individually. In current literature the method is mainly researched with a high-fidelity actuator line model (ALM). Because of the computational constraints imposed by this model, the effect of the Helix has not been researched for turbine arrays longer than 3. To investigate the effects of the Helix on a farm size scale, a lower fidelity model capturing the Helix is developed in this research. This model is based on a uniform actuator disk model and is called the H-ADM. The H-ADM is validated in laminar conditions at a fine resolution by comparing wake recovery to the ALM. The H-ADM captures both the additional wake mixing and wake displacement caused by the Helix. Furthermore, the H-ADM correctly predicts differences between the counterclockwise (CCW) and clockwise (CW) Helix. Due to modelling assumptions, the H-ADM can run simulations at a coarser resolution and with a smaller time-step than the ALM. Computational gains are achieved with the H-ADM as a result. This research shows that similar simulations are executed over 640 times faster for the H-ADM compared to ALM. The model is used to gain a deeper understanding of the mechanisms causing differences between the CCW and CW Helix. It turns out these differences fade away if no rotational force is exerted by the wind turbine. Finally, the computational gains of the H-ADM are leveraged by applying the Helix on the first row of a large scale wind farm with 48 turbines. For the considered farm the CCW Helix seems to outperform the CW Helix in terms of total power gains.