DOI: 10.11583/dtu.22739831.v1
title: Rødsand II wind-farm instantaneous LES flow field datasets and averaged power output

description: At EPFL, the WIRE-LES code, a well-established Large-Eddy Simulation (LES) code [1-3], is implemented to understand the flow physics better inside and in the wake of the Rødsand II wind-farm. The LES simulation of this wind-farm would provide important insights to the field measurement team. Time and space-averaged results help determine the most interesting locations for taking measurements. <br> The modelled wind-farm case considers prevalent offshore conditions in Denmark. A conventionally neutral boundary layer (CNBL) and a weak free atmosphere stratification level fixed at Gamma=1K/km are simulated. Rødsand II consists of 90 turbines manufactured by Siemens, SWT-2.3-93 of 2.3MW with a diameter D=93m and a hub height of z_h=68.5m [4-6]. The surface roughness is set to z_0=0.001m. The flow is driven by a geostrophic wind G=9.5m/s and the Coriolis parameter is equivalent to the latitude of the Rødsand II location, which is f_c=1.185e-4rad/s. The case is initialized with a constant streamwise velocity of 9.5m/s. The inflow to the windfarm is characterized by an 8.5m/s velocity and a 7% streamwise turbulence intensity at hub height. It is worth noting that the wind direction is West. <br> In the figure attached (Power_map.png), we can find the layout of the Rødsand II wind-farm and the colour indicates the time-averaged power output of each turbine. The plotted power output can be found in the 5x18 matrix attached (Rodsand2_avg_turb_power.mat ) which can be opened in MATLAB. <br> The .nc files contain the generated instantaneous flow field data every 1.2 seconds of the CNBL case over 10mins of real-time simulation, extracted in standard NetCDF format. The data is taken at three horizontal xy-planes: the hub height, top tip and lower tip height, where 'hub, 'top' and 'bottom' are the corresponding labels for each that can be found at the end of each .nc file. The streamwise velocity component 'u' is recorded. The naming convention would be: t_ts_u_top/hub/bottom.nc <br> The geometry used to model the wind-farm, and which is helpful to read the flow fields, is also attached as a text file where the x and y coordinates used in the LES model are listed in two columns (x/y). <br> Acknowledgements:<br> Computing resources were provided by EPFL through its Scientific IT and Application Support Center (SCITAS) and by the Swiss National Super-computing Centre (CSCS). <br> References: 1. Albertson, J.D., Parlange, M.B.: Surface length scales and shear stress: Implications for land-atmosphere interaction over complex terrain. Water Resources Research 35, 2121–2132 (1999). 2. Porté-Agel, F., Meneveau, C., Parlange, M.B.: A scale-dependent dynamic model for large-eddy simulation: application to a neutral atmospheric boundary layer. Journal of Fluid Mechanics 415(1), 261–284 (jul 2000). 3. Wu, Y.T., Porté-Agel, F.: Large-Eddy Simulation of Wind-Turbine Wakes: Evaluation of Turbine Parametrisations. Boundary-Layer Meteorology 138, 345–366 (2011). 4. Hansen, K.S., Réthoré, P.E., Palma, J., Hevia, B.G., Prospathopoulos, J., Pe ̃na, A., Ott, S., Schepers, G., Palomares, A., van der Laan, M.P., Volker, P.: Simulation of wake effects between two wind farms. Journal of Physics: Conference Series 625(1), 012008 (jun 2015). 5. der Laan, M.P.V., Hansen, K.S., Sørensen, N.N., Réthoré, P.E.: Predicting wind farm wake interaction with rans: an investigation of the coriolis force. Journal of Physics: Conference Series 625(1), 012026 (jun 2015). 6. Nygaard, N.G.: Wakes in very large wind farms and the effect of neighbouring wind farms. Journal of Physics: Conference Series 524(1), 012162 (jun 2014).