On the Effects of Directional Bin Size when Simulating Large Offshore Wind Farms with CFD

The most significant difference to an offshore wind farm resource assessment compared to onshore locations is the lower surface roughness values resulting from the lack of vegetation and terrain. As such, turbine wakes take longer to dissipate, and thus have a greater significance for the mean wind speeds and turbulence intensity encountered by turbines downstream. The greater influence of turbine wakes offshore, combined with the often regular turbine layouts of offshore farms, result in significant losses in power generation, and thus asset value, when the wind blows along a line of turbines. To reduce the risk to financial investment, computer simulations are often run to predict the expected wake losses of wind farms before they are built. As using Computational Fluid Dynamics (CFD) models to simulate numerous scenarios can be time consuming, it is important to use best practice to minimise the number of runs required to accurately capture the farm wake loss. This work investigates the number of simulations required to predict the production losses due to turbine wakes for a single scenario to an acceptable accuracy without compromising on the time required for such an investigation.