Large-Eddy Simulations of the Atmospheric Boundary Layer for Wind Energy Applications: Blockage and Extreme Events

Abstract

To sustain growth in wind electricity generation, research is needed to increase energy production and reduce lifetime costs of wind projects. Increasing energy production of wind plants requires reducing losses during the operation of wind turbines. Furthermore, reducing lifetime costs of wind projects deployed in regions with recurrent extreme weather events requires more robust design standards for wind turbines. This thesis seeks to improve our understanding of losses in large wind plants and assess design criteria for wind turbines that will be deployed in regions where tropical cyclones can occur frequently.

Wind plant blockage can reduce energy production of large wind plants. We use idealized large-eddy simulations (LES) of the atmospheric boundary layer to understand the physical cause of wind plant blockage and the mechanisms that amplify it. We find large vertical shear of the horizontal velocity amplifies wind plant blockage in stably stratified boundary layers. Because other physical mechanisms have also been identified to amplify blockage, we investigate the difficulties in measuring blockage in the field for model validation. We perform LES of a wind plant in Oklahoma, where lidar measurements will be used to quantify blockage in the future. We find that blockage can be wrongly characterized from lidar observations if flow inhomogeneities from varying terrain elevation are not considered.

Offshore wind deployment in the future is planned in regions where extreme storms can occur frequently, however current design standards for wind turbines can underestimate the extreme wind conditions in tropical cyclones. We use idealized LES to characterize the extreme wind conditions that wind turbines will experience in tropical cyclones. We find that winds in extreme storms are often more severe than as outlined in current design criteria for wind turbines.