Deficit budget analysis of turbulent wakes in the stratified atmospheric boundary layer

As wind energy penetration increases, it becomes critically important to ensure that the modeling tools used for siting, design, and control of wind energy are robust to uncertainty. To model wind power, physics-based analytical wake models are typically used, which simplify atmospheric boundary layer (ABL) and wake physics. This is accomplished primarily through the parameterization of turbulence, thus introducing model-form uncertainty. In this study, we systematically analyze the physical mechanisms relevant to turbulence in the wakes of wind turbines operating in the stratified ABL. We use large eddy simulation (LES) to study wind turbine wakes under a variety of atmospheric stability conditions. To parse the turbulence in the wake from the turbulent, incident ABL flow, we decompose the flow into the base ABL flow and the deficit flow produced by the turbine. We then analyze the decomposed flow field budgets to study the effects of changing stability on important quantities in the wake, such as the momentum, mean kinetic energy, and turbulent kinetic energy. We perform this analysis with the goals of formulating new physics-based models that incorporate these important atmospheric effects and quantifying the impact of their omission.