Wind power wake modelling : Development and application of an actuator disc method for industrial utilization

Abstract: As a wind turbine extracts energy from the wind it creates a region downstream where the wind velocity is decreased and the urbulence intensity is increased, this region is commonly called the wake region. Today’s wind farms include a large number of wind turbines position in tight layouts. These tight layouts result in increased power losses due to wakes, rendering accurate wind turbine wake modelling crucial in developing cost effective projects.The primary aim of this study is to create a method capable of conducting full-scale wind farm wake computations accurately in a time efficient manner by taking into account the computational resources and data availability of a typical industrial user. As a first step of this study, an actuator disc (ACD) method (old ACD) used within WindSim, is evaluated against power production data from the Lillgrund offshore wind. This study is followed by the development of a new ACD method. The new ACD method differs from the previous ACD method in terms of how the thrust distribution and the power production is calculated. A series of validation studies are performed on this newly introduced ACD method. These consist of validating the method against two cases with known analytical solutions, the research code EllipSys3D which uses Large Eddy Simulation (LES) based computations with an ACD approach and three differentwind tunnel set–ups. Lastly, a comparative analysis of the two ACD methods (old and new) and two analytical wake models is done using wind turbine power production data from Lillgrund.Results from the validation studies show that this new ACD method is able to predict the overall behaviour of the flow with low computational effort while also taking into account the availability of data for a typical industrial user. One may say that the new ACD method in RANS, which has much lower computational requirements than the ACD method in LES at the cost of lower accuracy, represents a good compromise. Lastly, the results from the new ACD method show a clear improvement in the estimated power production for the Lillgrund wind farm in comparison to the old ACD method.