Wind Farm Modeling: From the Meso-Scale to the Micro-Scale
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This dissertation is focused on numerical modeling of wind turbines. An initial set of simulations is performed to assess the effect of the tower and nacelle on the wake of a wind turbine. The wind turbine is modeled using the Actuator Line Model for the rotor and the Immersed Boundary Method for the tower and nacelle. Results are compared with the experimental measurements made at NTNU (Norwegian University of Science and Technology), and numerical simulations available in the literature. For the first time, we show that the tower and nacelle not only produce a velocity deficit in the wake but also affect the entrainment of mean kinetic energy. The wake of the tower interacts with that generated by the turbine blades, promoting the breakdown of the tip vortex and increasing the mean kinetic energy flux into the wake. Additionally, we studied the effect of topography on the performance and wake of a wind turbine. The topography consists of wavy ridges that are perpendicular to the flow direction. The effect of the relative position of the rotor and terrain geometry is assessed by placing the turbine either at the crest or trough of the undulating wall. To study wind turbines under realistic conditions, one-way nested mesoscale to microscale simulations of an on-shore wind farm have been performed using the Weather Research and Forecasting (WRF) model. Each simulation contains five nested domains modeling the mesoscale wind field using the planetary boundary layer scheme on the entire north Texas Panhandle region to microscale wind fluctuations and turbine wakes of a wind farm with Large-Eddy simulation (LES). Moreover, an additional nesting with our in-house LES code is performed. Numerical results agree well with meteorological, LiDAR and SCADA data. Power production and momentum deficit obtained with our in-house LES code and actuator disk model presented a better agreement than WRF because the simulation captures the wind shear on the rotor.