Large Eddy Simulation of Wind Turbine Wake Dynamics in the Stable Boundary Layer Using the Weather Research and Forecasting Model

Monday, 15 December 2014
Matthew Aitken, Environmental Protection Agency Research Triangle Park, Research Triangle Park, NC, United States, Branko Kosovic, National Center for Atmospheric Research, Boulder, CO, United States, Jeffrey D Mirocha, Lawrence Livermore Natl Lab, Livermore, CA, United States and Julie K Lundquist, U. of Colorado at Boulder, Boulder, CO, United States
To thoroughly verify the actuator disk model recently implemented in WRF for large eddy simulation (LES) of wind turbine wakes, simulations of various types of turbines and atmospheric conditions must be compared to full-scale field measurements of the real atmosphere. Here, numerical simulations are compared to nacelle-based scanning lidar measurements taken in stable atmospheric conditions during a field campaign conducted at a wind farm in the western United States. Using several wake characteristics—such as the velocity deficit, centerline location, and wake width—as metrics for model verification, the simulations show good agreement with the observations. Notably, the average velocity deficit was seen to be quite high in both the experiment and simulation, resulting from a low average wind speed and therefore high average turbine thrust coefficient. Moreover, new features—namely rotor tilt and drag from the nacelle and tower—were added to the existing actuator disk model in WRF-LES. Compared to the rotor, the effect of the tower and nacelle on the flow is relatively small but nevertheless important for an accurate representation of the entire turbine. Adding rotor tilt to the model causes the vertical location of the wake center to shift upward. Continued advancement of the actuator disk model in WRF-LES will help lead to optimized turbine siting and controls at wind farms.