Modeling of horizontal axis wind turbine wakes in Horns Rev offshore wind farm using an improved actuator disc model coupled with computational fluid dynamic

In order to increase the accuracy and ability to predict the total energy gained in wind farms, it is necessary to use accurate wake models. In the present study, an improved methodology is applied on actuator disc in order to take all the operational and geometrical characteristics into account such as airfoil type, angular velocity, twist, and chord distribution. In wind farms, turbines are affected by upstream ones resulting in a non-uniform upstream velocity for each turbine. However, in literature, for all the wind turbines in a wind farm, thrust coefficient curve at undisturbed wind speed is used in order to estimate the upstream speed resulting in some errors. This weakness of actuator disc is resolved by a hybrid methodology based on blade element momentum theory and mass conservation coupled with computational fluid dynamics to be independent of thrust coefficient curve and calculate more accurate incoming velocity according to operational condition. It has been observed that by using the developed model and considering the details of wind turbines and more accurate incoming wind speed, in spite of steady state simulation and low computational cost, the interaction between different turbines is well described. For turbulence modeling, standard k-epsilon turbulence model is used and it is shown that the error of power estimation in second row of turbines especially in 270 degrees wind angle is decreased significantly. In large wind sectors, such as 270 +/- 10 degrees, +/- 15 degrees, 222 +/- 10 degrees, +/- 15 degrees and 312 +/- 5 degrees, +/- 10 degrees the proposed model performs as well as LES simulation. The developed methodology is practical for designing and optimization of new wind farms even if the technical specifications such as thrust curve would not be available from manufacturer.