Numerical Simulation studies of very large wind farms: working at the interface bridging engineering and geophysics

Large Eddy Simulations (LES) of turbulent flows have proven to be valuable to better understand complex turbulent flows. The technique consists of solving the nonlinear partial differential equations governing fluid flow, the Navier-Stokes equations, down to some grid spacing that can be afforded with present-day computers, while parameterizing the smaller scales.Here we deploy this technique to better understand and develop engineering models for turbulent flow in very large wind farms. As wind energy is characterized by low power density, in order for wind energy to make a significant contribution to our overall energy supply, very large wind farms (on or off-shore) need to be envisioned. For very large wind farms, interesting couplings between individual turbines and the atmospheric boundary layer become crucial. This presentation will summarize our results that focus on understanding how wind turbines, when deployed in large arrays, extract kinetic energy from the atmospheric boundary layer. A suite of LES, in which wind turbines are modeled using the classical `actuator disk’ concept, are performed for various wind turbine arrangements, turbine loading factors, and surface roughness values. The results are used to develop improved models for effective roughness lengths and to obtain new predictions for optimal spacing distances among wind turbines in a large wind farm. We use the results also to develop a new wake superposition model, the coupled wake boundary layer (CWBL) approach as an update to the classic Jensen/Park model. It enables to capture the interactions of the turbine wakes with the atmosphere. This work is a collaboration with colleagues, postdocs and students involved in the WINDINSPIRE project and is supported by the US National Science Foundation.