On the effects of directional bin size when simulating large offshore wind farms with CFD

Abstract

Computational Fluid Dynamics (CFD) models are increasingly being used to simulate the flow through large wind farms to investigate scenarios with significant wake losses. This study investigates some of the effects caused by combining multiple simulation runs to represent the wide directional bin sizes sometimes required to ensure significant quantities of validation data and to account for wake meandering. CFD simulation results are combined using three different methods for six different directional bin sizes and compared against measurements from the Nysted offshore wind farm. Results show only small variation between averaging the model outputs uniformly or according to measured directional frequencies, whilst utilising a normal distribution reduces the variation between bin sizes. In addition, the greatest variation between results from combined multiple simulations compared to results from a single simulation occurs at the third turbine in a row. It is found that combined CFD results for the larger bin sizes are more accurate than the results for smaller bin sizes, when compared to the measured dataset with corresponding directional bin sizes.