Downstream Evolution of Eddy Viscosity in the Wake of a Wind Turbine

We propose a two-scale model for the streamwise development of eddy viscosity in the wake of a wind turbine which augments the curled wake model by separating the wake flow from the background and assigning each region independent viscosities. Measurements of eddy viscosity were obtained by fitting data from wind tunnel experiments conducted at Portland State University (PSU) and SOWFA LES simulations performed at the National Renewable Energy Lab (NREL). A range of yaw and tilt misalignment angles were considered to discern the impact of wake asymmetry from the curled wake. The downstream evolution of eddy viscosity is presented as a function of distance with emphasis on differences between near and far wake behavior. Additionally, variations in eddy viscosity formation are detailed in response to nacelle misalignment. The model is implemented in the NREL FLORIS wake modeling framework and demonstrates agreement with experimental and simulation data in capturing the dynamics of both wake regions.